TAMM: Tensor algebra for many-body methods.

Tensor algebra operations such as contractions in computational chemistry consume a significant fraction of the computing time on large-scale computing platforms. The widespread use of tensor contractions between large multi-dimensional tensors in describing electronic structure theory has motivated the development of multiple tensor algebra frameworks targeting heterogeneous computing platforms. In this paper, we present Tensor Algebra for Many-body Methods (TAMM), a framework for productive and performance-portable development of scalable computational chemistry methods. TAMM decouples the specification of the computation from the execution of these operations on available high-performance computing systems. With this design choice, the scientific application developers (domain scientists) can focus on the algorithmic requirements using the tensor algebra interface provided by TAMM, whereas high-performance computing developers can direct their attention to various optimizations on the underlying constructs, such as efficient data distribution, optimized scheduling algorithms, and efficient use of intra-node resources (e.g., graphics processing units). The modular structure of TAMM allows it to support different hardware architectures and incorporate new algorithmic advances. We describe the TAMM framework and our approach to the sustainable development of scalable ground- and excited-state electronic structure methods. We present case studies highlighting the ease of use, including the performance and productivity gains compared to other frameworks.

Ultra-Wide Band Gap Ga2O3-on-SiC MOSFETs.

Ultra-wide band gap semiconductor devices based on ß-phase gallium oxide (Ga2O3) offer the potential to achieve higher switching performance and efficiency and lower manufacturing cost than that of today's wide band gap power electronics. However, the most critical challenge to the commercialization of Ga2O3 electronics is overheating, which impacts the device performance and reliability. We fabricated a Ga2O3/4H-SiC composite wafer using a fusion-bonding method. A low-temperature (≤600 °C) epitaxy and device processing scheme was developed to fabricate MOSFETs on the composite wafer. The low-temperature-grown epitaxial Ga2O3 devices deliver high thermal performance (56% reduction in channel temperature) and a power figure of merit of (∼300 MW/cm2), which is the highest among heterogeneously integrated Ga2O3 devices reported to date. Simulations calibrated based on thermal characterization results of the Ga2O3-on-SiC MOSFET reveal that a Ga2O3/diamond composite wafer with a reduced Ga2O3 thickness (∼1 µm) and a thinner bonding interlayer (<10 nm) can reduce the device thermal impedance to a level lower than that of today's GaN-on-SiC power switches.

Optimized Quantum Phase Estimation for Simulating Electronic States in Various Energy Regimes.

While quantum algorithms for simulations exhibit better asymptotic scaling than their classical counterparts, they currently cannot be accurately implemented on real-world devices. Instead, chemists and computer scientists rely on costly classical simulations of these quantum algorithms. In particular, the quantum phase estimation (QPE) algorithm is among several approaches that has attracted much attention in recent years due to its genuine quantum character. However, it is memory-intensive to simulate and intractable for moderate system sizes. This paper discusses the performance and applicability of QPESIM, a new simulation of the QPE algorithm designed to take advantage of modest computational resources. In particular, we demonstrate the versatility of QPESIM in simulating various electronic states by examining the ground and core-level states of H2O. For these states, we also discuss the effect of the active-space size on the quality of the calculated energies. For the high-energy core-level states, we demonstrate that new QPE simulations for active spaces defined by 15 active orbitals significantly reduce the errors in core-level excitation energies compared to earlier QPE simulations using smaller active spaces.

BOA: A partitioned view of genome assembly.

De novo genome assembly is a fundamental problem in computational molecular biology that aims to reconstruct an unknown genome sequence from a set of short DNA sequences (or reads) obtained from the genome. The relative ordering of the reads along the target genome is not known a priori, which is one of the main contributors to the increased complexity of the assembly process. In this article, with the dual objective of improving assembly quality and exposing a high degree of parallelism, we present a partitioning-based approach. Our framework, BOA (bucket-order-assemble), uses a bucketing alongside graph- and hypergraph-based partitioning techniques to produce a partial ordering of the reads. This partial ordering enables us to divide the read set into disjoint blocks that can be independently assembled in parallel using any state-of-the-art serial assembler of choice. Experimental results show that BOA improves both the overall assembly quality and performance.

Assessment of Plasmodium falciparum histidine rich protein 2 and /3 (pfhrp 2&/ pfhrp 3) gene deletion or mutation in Plasmodium falciparum positive blood samples in a tertiary care centre in South India.

Rapid diagnostic card tests (RDTs) enable timely and appropriate diagnosis of malaria especially in remote areas. Plasmodium falciparum histidine rich protein 2 (PFHRP2) is the most targeted antigen for the detection of Plasmodium falciparum infections by rapid diagnostic card test. Genetic mutations and gene deletions are important emerging factors for false-negative RDTs, which may delay the provision of life-saving treatment for the patients. Hence, we would like to evaluate for the existence of pfhrp2/3 gene deleted P. falciparum parasites in our health care setting. This study was conducted for a period of 2 years in a tertiary care centre in South India. Blood samples that are microscopically confirmed as P. falciparum but negative by RDT were assessed for the presence of pfhrp2, pfhrp3, and their flanking genes using conventional PCR. Follow up of the clinical outcomes were also done for these patients. Of the 63 positive samples collected (50 /63) 79.4% were P.vivax and (13/63) 20.6% were P.falciparum by PCR. Among the 13 P. falciparum positive samples, 4 samples (4/13), (95% CI -10.36% to 61.11%) were found to be RDT negative but microscopically positive.Pfhrp2,pfhrp3 and their flanking genes were amplified for these 4 samples. All 4 samples were found to be negative for both pfhrp2-2 & pfhrp2-3 exon regions and also varying patterns of flanking gene deletions were also noted.This study provides molecular evidence for the existence of pfhrp2 & pfhrp3 deleted P. falciparum parasites in a tertiary care centre in South India warranting periodic evaluation of pfhrp2 based RDT use. Only pfhrp2/3 RDT based decision on diagnosis of P.falciparum malaria should always be reconsidered especially in remote areas.

Plasmon-Phonon Coupling in Electrostatically Gated ß-Ga2O3 Films with Mobility Exceeding 200 cm2 V-1 s-1.

Monoclinic ß-Ga2O3, an ultra-wide bandgap semiconductor, has seen enormous activity in recent years. However, the fundamental study of the plasmon-phonon coupling that dictates electron transport properties has not been possible due to the difficulty in achieving higher carrier density (without introducing chemical disorder). Here, we report a highly reversible, electrostatic doping of ß-Ga2O3 films with tunable carrier densities using ion-gel-gated electric double-layer transistor configuration. Combining temperature-dependent Hall effect measurements, transport modeling, and comprehensive mobility calculations using ab initio based electron-phonon scattering rates, we demonstrate an increase in the room-temperature mobility to 201 cm2 V-1 s-1 followed by a surprising decrease with an increasing carrier density due to the plasmon-phonon coupling. The modeling and experimental data further reveal an important "antiscreening" (of electron-phonon interaction) effect arising from dynamic screening from the hybrid plasmon-phonon modes. Our calculations show that a significantly higher room-temperature mobility of 300 cm2 V-1 s-1 is possible if high electron densities (>1020 cm-3) with plasmon energies surpassing the highest energy LO mode can be realized. As Ga2O3 and other polar semiconductors play an important role in several device applications, the fundamental understanding of the plasmon-phonon coupling can lead to the enhancement of mobility by harnessing the dynamic screening of the electron-phonon interactions.

Effect of extended defects on photoluminescence of gallium oxide and aluminum gallium oxide epitaxial films.

In this work, a systematic photoluminescence (PL) study on three series of gallium oxide/aluminum gallium oxide films and bulk single crystals is performed including comparing doping, epitaxial substrates, and aluminum concentration. It is observed that blue/green emission intensity strongly correlates with extended structural defects rather than the point defects frequently assumed. Bulk crystals or Si-doped films homoepitaxially grown on (010) ß-Ga2O3 yield an intense dominant UV emission, while samples with extended structural defects, such as gallium oxide films grown on either (-201) ß-Ga2O3 or sapphire, as well as thick aluminum gallium oxide films grown on either (010) ß-Ga2O3 or sapphire, all show a very broad PL spectrum with intense dominant blue/green emission. PL differences between samples and the possible causes of these differences are analyzed. This work expands previous reports that have so far attributed blue and green emissions to point defects and shows that in the case of thin films, extended defects might have a prominent role in emission properties.

Post-transurethral resection of prostate urethral strictures: Are they often underreported? A single-center retrospective observational cohort study.

OBJECTIVES: Post-transurethral resection of prostate urethral stricture (PTS) is a well-documented delayed complication following transurethral resection of the prostate (TURP). The aim is to analyze various risk factors of PTS and see if the overall incidence is underreported. MATERIALS AND METHODS: A retrospective study was conducted in our institution between January 2017 and December 2018 in men who underwent TURP. Data obtained from the medical records department were analyzed. Statistical analysis was done using Fisher's exact test. A two-tailed P < 0.05 is considered statistically significant. RESULTS: Of the 447 men who underwent TURP, 57 developed PTS. Fifteen of 334 patients who underwent calibration before the procedure developed stricture compared to 42 of 137 without calibration (P < 0.01). There was a significantly lesser incidence of stricture with 24 Fr resectoscope compared with 26 Fr sheath (P < 0.04). Two patients with 24 Fr Foley and 30 of 35 (86%) patients with 22 Fr Foley catheter developed stricture of urethra. Distal bulbar urethra was the most common site of narrowing following TURP. Eighteen patients had Salvaris swab placed for traction and 12 patients required full-thigh traction, of which majority developed meatal stenosis. CONCLUSIONS: TURP is one of the common surgical procedures performed by urologists. Meatitis and meatal stenosis, if included as complications of TURP, would increase the overall incidence of PTS. Factors such as the size of resectoscope sheath used, size of catheter inserted, placement of Salvaris swab traction, and preoperative calibration of urethra have a significant impact on the ultimate outcome.

Spalling-Induced Liftoff and Transfer of Electronic Films Using a van der Waals Release Layer.

Heterogeneous integration strategies are increasingly being employed to achieve more compact and capable electronics systems for multiple applications including space, electric vehicles, and wearable and medical devices. To enable new integration strategies, the growth and transfer of thin electronic films and devices, including III-nitrides, metal oxides, and 2D materials, using 2D boron nitride (BN)-on-sapphire templates are demonstrated. The van der Waals (vdW) BN layer, in this case, acts as a preferred mechanical release layer for precise separation at the substrate-film interface and leaves a smooth surface suitable for vdW bonding. A tensilely stressed Ni layer sputtered on top of the film induces controlled spalling fracture that propagates at the BN/sapphire interface. By incorporating controlled spalling, the process yield and sensitivity are greatly improved, owed to the greater fracture energy provided by the stressed metal layer relative to a soft tape or rubber stamp. With stress playing a critical role in this process, the influence of residual stress on detrimental cracking and bowing is investigated. Additionally, a back-end selected area lift-off technique is developed which allows for isolation and transfer of individual devices or arbitrary shapes.

Isolated ureteral extrauterine endometrial stromal sarcoma: an unusual presentation.

Extrauterine endometrial stromal sarcomas (EUESSs) are rare tumours occurring without primary uterine involvement. They are classified as primary or secondary, depending on uterine involvement by stromal sarcomas. A 56-year-old woman who earlier underwent bilateral modified radical mastectomy for adenocarcinoma and total abdominal hysterectomy for endometrial stromal sarcoma, followed by tamoxifen therapy, presented with left loin pain. On evaluation, she had a left renal calculus with hydroureteronephrosis. Before percutaneous nephrolithotripsy, ureteroscopy revealed a polypoidal mass that was diagnosed as EUESS. The mass arose primarily within the ureteral lumen, with periureteric tissue uninvolved. She underwent left radical nephroureterectomy with adjuvant hormonal treatment. This is probably the first case of EUESS arising de novo from within the ureteral lumen without endometriosis, to be reported in medical literature. Immunohistochemistry facilitates earlier diagnosis. Cytoreductive surgery is the definitive treatment and multidisciplinary approach helps in overall survival of the patient.

Ga2O3-on-SiC Composite Wafer for Thermal Management of Ultrawide Bandgap Electronics.

ß-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor (EG ∼ 4.8 eV), which promises generational improvements in the performance and manufacturing cost over today's commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga2O3 device technologies. In this work, a novel Ga2O3/4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga2O3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm2/Vs and a volume charge of ∼3 × 1017 cm-3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga2O3/4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga2O3/4H-SiC interface is dominated by the thickness of the SiNx bonding layer and an unintentionally formed SiOx interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 µm thick Ga2O3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga2O3 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.

Thermal Conductivity of ß-Phase Ga2O3 and (AlxGa1-x)2O3 Heteroepitaxial Thin Films.

Heteroepitaxy of ß-phase gallium oxide (ß-Ga2O3) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of (2̅01)-oriented ß-Ga2O3 heteroepitaxial thin films were investigated. Unintentionally doped ß-Ga2O3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward ⟨112̅0⟩ via metal-organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the ß-Ga2O3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the ß-Ga2O3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick ß-Ga2O3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye-Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of ß-Ga2O3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the ß-Ga2O3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the ß-Ga2O3/sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown (2̅01)-oriented ß-(AlxGa1-x)2O3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the ß-(AlxGa1-x)2O3 films exhibit lower thermal conductivities (2.8-4.7 W/m·K) than the ß-Ga2O3 thin films. The dominance of the alloy disorder scattering in ß-(AlxGa1-x)2O3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown ß-phase Ga2O3 and (AlxGa1-x)2O3 thin films and lays the groundwork for the thermal modeling and design of ß-Ga2O3 electronic and optoelectronic devices.

Bilateral acute pyelonephritis with left renal artery aneurysm as a cause of bilateral spontaneous subcapsular haematoma: lessons learnt.

Forniceal ruptures after acute pyelonephritis are relatively common. Bilateral spontaneous subcapsular haematoma (SSCH) is an uncommon sequela to pyelonephritis. We report a case of SSCH where the underlying cause of haematoma was a vascular anomaly. A 38-year-old woman with diabetes presented with fever, flank pain and shock following cystoscopy and Double J stenting done elsewhere. CT abdomen showed left subcapsular renal haematoma, managed by pigtail insertion. Postoperative CT showed right renal subcapsular haematoma and left moderate renal subcapsular haematoma. Renal angiogram showed pseudo-aneurysm on the left middle polar artery for which selective embolisation was performed. Physicians and urologists who come across SSCH for which no definite aetiology could be identified should keep in mind the possibility of an underlying vascular anomaly that could precipitate such a condition. The purpose of this report is to highlight the importance of remembering vascular causes in such unexplained cases of SSCH.

From NWChem to NWChemEx: Evolving with the Computational Chemistry Landscape.

Since the advent of the first computers, chemists have been at the forefront of using computers to understand and solve complex chemical problems. As the hardware and software have evolved, so have the theoretical and computational chemistry methods and algorithms. Parallel computers clearly changed the common computing paradigm in the late 1970s and 80s, and the field has again seen a paradigm shift with the advent of graphical processing units. This review explores the challenges and some of the solutions in transforming software from the terascale to the petascale and now to the upcoming exascale computers. While discussing the field in general, NWChem and its redesign, NWChemEx, will be highlighted as one of the early codesign projects to take advantage of massively parallel computers and emerging software standards to enable large scientific challenges to be tackled.

Toward Quantum Computing for High-Energy Excited States in Molecular Systems: Quantum Phase Estimations of Core-Level States.

This paper explores the utility of the quantum phase estimation (QPE) algorithm in calculating high-energy excited states characterized by the promotion of electrons occupying core-level shells. These states have been intensively studied over the last few decades, especially in supporting the experimental effort at light sources. Results obtained with QPE are compared with various high-accuracy many-body techniques developed to describe core-level states. The feasibility of the quantum phase estimator in identifying classes of challenging shake-up states characterized by the presence of higher-order excitation effects is discussed. We also demonstrate the utility of the QPE algorithm in targeting excitations from specific centers in a molecule. Lastly, we discuss how the lowest-order Trotter formula can be applied to reducing the complexity of the ansatz without affecting the error.

Prognostic scoring system and risk stratification in patients with emphysematous pyelonephritis: an 11-year prospective study at a tertiary referral centre.

OBJECTIVES: To define pre-morbid, clinical, laboratory, and imaging features and identify prognostic factors associated with morbidity and mortality in patients with emphysematous pyelonephritis (EPN) and develop a prognostic scoring system for improving management outcomes. PATIENTS AND METHODS: From January 2009 to December 2019, we performed a prospective study of all patients with a suspected diagnosis of EPN referred to a specialist tertiary centre in South India. All patients who underwent non-contrast computed tomography of the abdomen and those diagnosed with EPN were included in this study. Demographic parameters, imaging, haematological and microbiology results were recorded. Patients were divided into three groups: Group 1, patients who survived without any intervention; Group 2, those who survived with surgical intervention; and Group 3, those who died with or without intervention. A prognostic scoring system was developed from 18 different parameters and risk stratification was developed. The scores were correlated with overall prognosis. RESULTS: Data from 131 patients with EPN enrolled in the study were analysed: Group 1 (n = 22), Group 2 (n = 102) and Group 3 (n = 7). By using univariate analysis, 10 factors were identified to be significantly associated with prognosis. Diabetes mellitus was the most common comorbidity. Shock at initial admission indicated a poor prognosis and warranted immediate attention (P < 0.001). CONCLUSIONS: A multi-disciplinary approach, a high index of clinical suspicion, an early diagnosis and administration of culture-specific antibiotics with identification of prognostic indicators and risk stratification, allows prompt and appropriate medical and surgical treatments that could improve EPN management outcomes.

Cellular growth factors as prospective therapeutic targets for combination therapy in androgen independent prostate cancer (AIPC).

Cancer is the second leading cause of death worldwide, with prostate cancer, the second most commonly diagnosed cancer among men. Prostate cancer develops in the peripheral zone of the prostate gland, and the initial progression largely depends on androgens, the male reproductive hormone that regulates the growth and development of the prostate gland and testis. The currently available treatments for androgen dependent prostate cancer are, however, effective for a limited period, where the patients show disease relapse, and develop androgen-independent prostate cancer (AIPC). Studies have shown various intricate cellular processes such as, deregulation in multiple biochemical and signaling pathways, intra-tumoral androgen synthesis; AR over-expression and mutations and AR activation via alternative growth pathways are involved in progression of AIPC. The currently approved treatment strategies target a single cellular protein or pathway, where the cells slowly develop resistance and adapt to proliferate via other cellular pathways over a period of time. Therefore, an increased research aims to understand the efficacy of combination therapy, which targets multiple interlinked pathways responsible for acquisition of resistance and survival. The combination therapy is also shown to enhance efficacy as well as reduce toxicity of the drugs. Thus, the present review focuses on the signaling pathways involved in the progression of AIPC, comprising a heterogeneous population of cells and the advantages of combination therapy. Several clinical and pre-clinical studies on a variety of combination treatments have shown beneficial outcomes, yet further research is needed to understand the potential of combination therapy and its diverse strategies.

Green's function coupled cluster simulation of the near-valence ionizations of DNA-fragments.

Accurate description of the ionization process in DNA is crucial to the understanding of the DNA damage under exposure to ionizing radiation and the exploration of the potential application of DNA strands in nanoelectronics. In this work, by employing our recently developed Green's function coupled-cluster library on supercomputing facilities, we have studied the spectral functions of several guanine-cytosine (G-C) base pair structures ([G-C]n, n = 1-3) for the first time in a relatively broad near-valence regime ([-25.0, -5.0] eV) in the coupled-cluster with singles and doubles level. Our focus is to give a preliminary many-body coupled-cluster understanding and guideline of the vertical ionization energy (VIE), spectral profile, and ionization feature changes of these systems as the system size expands in this near-valence regime. The results show that, as the system size expands, even though the lowest VIEs keep decreasing, the changes of spectral function profile and the relative peak positions get unexpectedly smaller. Further analysis of the ionized states associated with the most intensive peak in the spectral functions reveals non-negligible |2h, 1p⟩'s in the ionized wave functions of the considered G-C base pair systems. The leading |2h, 1p⟩'s associated with the main ionizations from the cytosine part of the G-C base pairs feature a transition from the intra-base-pair cytosine π → π* excitation to the inter-base-pair electron excitation as the size of G-C base pairs expands, which also indicates the minimum quantum region in the many-body calculations of DNA systems.

Urogenital tuberculosis - epidemiology, pathogenesis and clinical features.

Tuberculosis (TB) is the most common cause of death from infectious disease worldwide. A substantial proportion of patients presenting with extrapulmonary TB have urogenital TB (UG-TB), which can easily be overlooked owing to non-specific symptoms, chronic and cryptic protean clinical manifestations, and lack of clinician awareness of the possibility of TB. Delay in diagnosis results in disease progression, irreversible tissue and organ damage and chronic renal failure. UG-TB can manifest with acute or chronic inflammation of the urinary or genital tract, abdominal pain, abdominal mass, obstructive uropathy, infertility, menstrual irregularities and abnormal renal function tests. Advanced UG-TB can cause renal scarring, distortion of renal calyces and pelvic, ureteric strictures, stenosis, urinary outflow tract obstruction, hydroureter, hydronephrosis, renal failure and reduced bladder capacity. The specific diagnosis of UG-TB is achieved by culturing Mycobacterium tuberculosis from an appropriate clinical sample or by DNA identification. Imaging can aid in localizing site, extent and effect of the disease, obtaining tissue samples for diagnosis, planning medical or surgical management, and monitoring response to treatment. Drug-sensitive TB requires 6-9 months of WHO-recommended standard treatment regimens. Drug-resistant TB requires 12-24 months of therapy with toxic drugs with close monitoring. Surgical intervention as an adjunct to medical drug treatment is required in certain circumstances. Current challenges in UG-TB management include making an early diagnosis, raising clinical awareness, developing rapid and sensitive TB diagnostics tests, and improving treatment outcomes.

Downfolding of many-body Hamiltonians using active-space models: Extension of the sub-system embedding sub-algebras approach to unitary coupled cluster formalisms.

In this paper, we discuss the extension of the recently introduced subsystem embedding subalgebra coupled cluster (SES-CC) formalism to unitary CC formalisms. In analogy to the standard single-reference SES-CC formalism, its unitary CC extension allows one to include the dynamical (outside the active space) correlation effects in an SES induced complete active space (CAS) effective Hamiltonian. In contrast to the standard single-reference SES-CC theory, the unitary CC approach results in a Hermitian form of the effective Hamiltonian. Additionally, for the double unitary CC (DUCC) formalism, the corresponding CAS eigenvalue problem provides a rigorous separation of external cluster amplitudes that describe dynamical correlation effects-used to define the effective Hamiltonian-from those corresponding to the internal (inside the active space) excitations that define the components of eigenvectors associated with the energy of the entire system. The proposed formalism can be viewed as an efficient way of downfolding many-electron Hamiltonian to the low-energy model represented by a particular choice of CAS. In principle, this technique can be extended to any type of CAS representing an arbitrary energy window of a quantum system. The Hermitian character of low-dimensional effective Hamiltonians makes them an ideal target for several types of full configuration interaction type eigensolvers. As an example, we also discuss the algebraic form of the perturbative expansions of the effective DUCC Hamiltonians corresponding to composite unitary CC theories and discuss possible algorithms for hybrid classical and quantum computing. Given growing interest in quantum computing, we provide energies for H2 and Be systems obtained with the quantum phase estimator algorithm available in the Quantum Development Kit for the approximate DUCC Hamiltonians.