Serum vascular endothelial growth factor affects tissue fluid accumulation and is associated with deteriorating tissue perfusion and oxygenation in severe sepsis: a prospective observational study.

BACKGROUND: Positive fluid balance and tissue fluid accumulation are associated with adverse outcomes in sepsis. Vascular endothelial growth factor (VEGF) increases in sepsis, promotes vascular permeability, and may affect tissue fluid accumulation and oxygenation. We used near-infrared spectroscopy (NIRS) to estimate tissue hemoglobin (Hb) oxygenation and water (H2O) levels to investigate their relationship with serum VEGF levels. MATERIAL AND METHODS: New-onset severe sepsis patients admitted to the intensive care unit were enrolled. Relative tissue concentrations of oxy-Hb ([HbO2]), deoxy-Hb ([HbR]), total Hb ([HbT]), and H2O ([H2O]) were estimated by near-infrared spectroscopy (NIRS) for three consecutive days and serum VEGF levels were measured. Comparisons between oliguric and non-oliguric patients were conducted and the correlations between variables were analyzed. RESULTS: Among 75 eligible patients, compared with non-oliguric patients, oliguric patients were administrated more intravascular fluids (median [IQR], 1926.00 [1348.50-3092.00] mL/day vs. 1069.00 [722.00-1486.75] mL/day, p < 0.001) and had more positive daily net intake and output (mean [SD], 1,235.06 [1303.14] mL/day vs. 313.17 [744.75] mL/day, p = 0.012), lower [HbO2] and [HbT] over the three-day measurement (analyzed by GEE p = 0.01 and 0.043, respectively) and significantly higher [H2O] on the third day than on the first two days (analyzed by GEE p = 0.034 and 0.018, respectively). Overall, serum VEGF levels were significantly negatively correlated with [HbO2] and [HbT] (rho = - 0.246 and - 0.266, p = 0.042 and 0.027, respectively) but positively correlated with [H2O] (rho = 0.449, p < 0.001). Subgroup analysis revealed a significant correlation between serum VEGF and [H2O] in oliguric patients (rho = 0.532, p = 0.003). Multiple regression analysis determined the independent effect of serum VEGF on [H2O] (standardized coefficient = 0.281, p = 0.038). CONCLUSIONS: In severe sepsis, oliguria relates to higher positive fluid balance, lower tissue perfusion and oxygenation, and progressive tissue fluid accumulation. Elevated serum VEGF is associated with worsening tissue perfusion and oxygenation and independently affects tissue fluid accumulation.

Recurrent right hepatic artery pseudoaneurysm after robotic-assisted cholecystectomy in a patient with Mirizzi syndrome: a case report.

BACKGROUND: Iatrogenic hepatic artery pseudoaneurysm is a rare complication following laparoscopic cholecystectomy. Trans-arterial embolization (TAE) is an effective way to control bleeding after a ruptured aneurysm. But uncommonly, rebleeding may occur which will require a second embolization or even laparotomy. CASE PRESENTATION: We report a case of a 45-year-old woman who underwent robotic-assisted cholecystectomy after the diagnosis of type II Mirizzi syndrome. During the operation, the anterior branch of the right hepatic artery was damaged and Hem-o-lok clips were applied to control the bleeding. The postoperative course was smooth, and the patient was discharged 6 days after the procedure. However, one week after hospital discharge, she presented to the emergency department with right upper abdominal tenderness, melena, and jaundice. After examination, the computed tomography angiography (CTA) revealed a 3 cm pseudoaneurysm at the distal stump of the right hepatic artery anterior branch. TAE with gelfoam material was performed. Three days later, the patient had an acute onset of abdominal pain. A recurrent pseudoaneurysm was found at the same location. She underwent TAE again but this time with a steel coil. No further complication was noted, and she was discharged one week later. CONCLUSIONS: Even with the assistance of modern technologies such as the robotic surgery system, one should still take extra caution while handling the vessels. Also, embolization of the pseudoaneurysm with steel coils may be suitable for preventing recurrence.

Inferior Vena Cava Volume Is an Independent Predictor of Massive Transfusion in Patients With Trauma.

OBJECTIVES: Early adequate resuscitation of patients with trauma is crucial in preventing shock and early mortality. Thus, we aimed to determine the performance of the inferior vena cava (IVC) volume and other risk factors and scores in predicting massive transfusion and mortality. METHODS: We included all patients with trauma who underwent computed tomography (CT) scan of the torso, which included the abdominal area, in our emergency department (ED) from January 2014 to January 2017. We calculated the 3-dimensional IVC volume from the left renal vein to the IVC bifurcation. The primary outcome was the performance of IVC volume in predicting massive transfusion, and the secondary outcome was the performance of IVC volume in predicting 24-hour and 30-day in-hospital mortality. RESULTS: Among the 236 patients with trauma, 7.6% received massive transfusions. The IVC volume and revised trauma score (RTS) were independent predictors of massive transfusion (adjusted odds ratio [OR]: 0.79 vs 1.86, 95% confidence interval [CI], 0.71-0.89 vs 1.4-2.47, respectively). Both parameters showed the good area under the curve (AUC) for the prediction of massive transfusion (adjusted AUC: 0.83 and 0.82, 95% CI, 0.74-0.92 vs 0.72-0.93, respectively). Patients with a large IVC volume (fourth quartile) were less likely to receive massive transfusion than those with a small IVC volume (first quartile, ≥28.29 mL: 0% vs <15.08 mL: 20.3%, OR: 0.13, 95% CI, 0.03-0.66). CONCLUSIONS: The volume of IVC measured on CT scan and RTS are independent predictors of massive transfusion in patients with trauma in the ED.

Diagnosis of a maxillary sinus fungus ball without intralesional hyperdensity on computed tomography.

OBJECTIVES/HYPOTHESIS: Maxillary sinus fungus ball (MSFB) is the most common type of noninvasive fungal rhinosinusitis. Surgical removal of the ball achieves good outcomes. Making a rapid and accurate diagnosis is important to avoid unnecessary medical therapy. Intralesional hyperdensity (IH) on computed tomography (CT) is reportedly a good indicator. The aim of this study was to evaluate the diagnostic features of MSFB without IH on preoperative CT images. STUDY DESIGN: Retrospective database review. METHODS: Two hundred fifty-eight patients with histopathological evidence of a sinus fungal ball were retrospectively investigated. Forty-seven of 222 patients with MSFB did not show IH on preoperative CT images and were enrolled in the MSFB group. Forty-one patients with unilateral nonfungal chronic rhinosinusitis were enrolled in a control group. CT features previously reported to have diagnostic significance were evaluated. RESULTS: Sclerosis of the lateral sinus wall, erosion of the inner sinus wall, and irregular surface of the material were significantly more common in the MSFB group than in the control group. In the subgroup of patients with total opacification in the maxillary sinus, the sensitivity, specificity, and positive and negative predictive values for erosion of the inner sinus wall were more than 90%. In the subgroup with partial opacification, the sensitivity, specificity, and positive predictive value of an irregular surface of the material were more than 80%. CONCLUSIONS: We have devised an algorithm to help diagnose MSFB without IH on preoperative CT images. Use of this algorithm would improve the diagnostic accuracy and ensure appropriate treatment. LEVEL OF EVIDENCE: 4 Laryngoscope, 129:1041-1045, 2019.

Erratum: Activate lattice oxygen redox reactions in metal oxides to catalyse oxygen evolution.

This corrects the article DOI: 10.1038/nchem.2695.

Modeling of the oxygen reduction reaction for dense LSM thin films.

In the present study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La1-xSrx)yMnO3±Î´ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation on the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.

Quantitative interpretation of impedance spectroscopy data on porous LSM electrodes using X-ray computed tomography and Bayesian model-based analysis.

It is broadly understood that strontium-doped lanthanum manganate (LSM) cathodes for solid oxide fuel cells (SOFCs) have two pathways for the reduction of oxygen: a surface-mediated pathway culminating in oxygen incorporation into the electrolyte at the triple-phase boundary (TPB), and a bulk-mediated pathway involving oxygen transfer across the electrode-electrolyte interface. Patterned electrode and thin film experiments have shown that both pathways are active in LSM. Porous electrode geometries more commonly found in SOFCs have not been amenable for precise measurement of active electrode width because of the difficulty in precisely measuring the electrode geometry. This study quantitatively compares a reaction-diffusion model for the oxygen reduction reaction in LSM to the impedance spectrum of an experimental LSM porous electrode symmetric button cell on a yttria-stabilized zirconia (YSZ) electrolyte. The porous microstructure was characterized using computed tomography (nano-CT) and Bayesian model-based analysis (BMA) was used to estimate model parameters. BMA produced good fits to the data, with higher than expected values for the interfacial capacitance at the LSM-YSZ interface and vacancy diffusion activation energy; these results may indicate that the active width of the electrode is on a similar scale with that of the space-charge width at the LSM-YSZ interface. The analysis also showed that the active width and proportion of current moving through the bulk pathway is temperature dependent, in accordance with patterned electrode results.

Addendum: Activating lattice oxygen redox reactions in metal oxides to catalyse oxygen evolution.

This corrects the article DOI: 10.1038/nchem.2695.

Activating lattice oxygen redox reactions in metal oxides to catalyse oxygen evolution.

Understanding how materials that catalyse the oxygen evolution reaction (OER) function is essential for the development of efficient energy-storage technologies. The traditional understanding of the OER mechanism on metal oxides involves four concerted proton-electron transfer steps on metal-ion centres at their surface and product oxygen molecules derived from water. Here, using in situ 18O isotope labelling mass spectrometry, we provide direct experimental evidence that the O2 generated during the OER on some highly active oxides can come from lattice oxygen. The oxides capable of lattice-oxygen oxidation also exhibit pH-dependent OER activity on the reversible hydrogen electrode scale, indicating non-concerted proton-electron transfers in the OER mechanism. Based on our experimental data and density functional theory calculations, we discuss mechanisms that are fundamentally different from the conventional scheme and show that increasing the covalency of metal-oxygen bonds is critical to trigger lattice-oxygen oxidation and enable non-concerted proton-electron transfers during OER.

Correlation of nanoscale behaviour of forces and macroscale surface wettability.

In this manuscript, we demonstrate a method based on atomic force microscopy which enables local probing of surface wettability. The maximum pull-off force, obtained from force spectroscopy shows a remarkable correlation with the macroscopically observed water contact angle, measured over a wide variety of surfaces starting from hydrophilic, all the way through to hydrophobic ones. This relationship, consequently, facilitates the establishment of a universal behaviour. The adhesion forces scale with the polar component of surface energy. However, no such relation could be established with the dispersive component. Hence, we postulate that the force(s) which enable us to correlate the force spectroscopy data measured on the nanoscale to the macroscopic contact angle are primarily arising from electrostatic-dipole-dipole interactions at the solid-liquid interface. London forces play less of a role. This effect in is line with density functional theory (DFT) calculations suggesting a higher degree of hydroxylation of hydrophilic surfaces. This result shows that molecular simulations and measurements on an atomic scale can be extrapolated to macroscopic surface wetting problems.

Oxygen Point Defect Chemistry in Ruddlesden-Popper Oxides (La1-xSrx)2MO4±Î´ (M = Co, Ni, Cu).

Stability of oxygen point defects in Ruddlesden-Popper oxides (La1-xSrx)2MO4±Î´ (M = Co, Ni, Cu) is studied with density functional theory calculations to determine their stable sites, charge states, and energetics as functions of Sr content (x), transition metal (M), and defect concentration (δ). We demonstrate that the dominant O point defects can change between oxide interstitials, peroxide interstitials, and vacancies. In general, increasing x and atomic number of M stabilizes peroxide over oxide interstitials as well as vacancies over both peroxide and oxide interstitials; increasing δ destabilizes both oxide interstitials and vacancies but barely affects peroxide interstitials. We also demonstrate that the O 2p-band center is a powerful descriptor for these materials and correlates linearly with the formation energy of all defects. The trends of formation energy versus x, M, and δ and the correlation with O 2p-band center are explained in terms of oxidation chemistry and electronic structure.

Catalytic Activity and Stability of Oxides: The Role of Near-Surface Atomic Structures and Compositions.

Electrocatalysts play an important role in catalyzing the kinetics for oxygen reduction and oxygen evolution reactions for many air-based energy storage and conversion devices, such as metal-air batteries and fuel cells. Although noble metals have been extensively used as electrocatalysts, their limited natural abundance and high costs have motivated the search for more cost-effective catalysts. Oxides are suitable candidates since they are relatively inexpensive and have shown reasonably high activity for various electrochemical reactions. However, a lack of fundamental understanding of the reaction mechanisms has been a major hurdle toward improving electrocatalytic activity. Detailed studies of the oxide surface atomic structure and chemistry (e.g., cation migration) can provide much needed insights for the design of highly efficient and stable oxide electrocatalysts. In this Account, we focus on recent advances in characterizing strontium (Sr) cation segregation and enrichment near the surface of Sr-substituted perovskite oxides under different operating conditions (e.g., high temperature, applied potential), as well as their influence on the surface oxygen exchange kinetics at elevated temperatures. We contrast Sr segregation, which is associated with Sr redistribution in the crystal lattice near the surface, with Sr enrichment, which involves Sr redistribution via the formation of secondary phases. The newly developed coherent Bragg rod analysis (COBRA) and energy-modulated differential COBRA are uniquely powerful ways of providing information about surface and interfacial cation segregation at the atomic scale for these thin film electrocatalysts. In situ ambient pressure X-ray photoelectron spectroscopy (APXPS) studies under electrochemical operating conditions give additional insights into cation migration. Direct COBRA and APXPS evidence for surface Sr segregation was found for La1-xSrxCoO3-δ and (La1-ySry)2CoO4±Î´/La1-xSrxCoO3-δ oxide thin films, and the physical origin of segregation is discussed in comparison with (La1-ySry)2CoO4±Î´/La1-xSrxCo0.2Fe0.8O3-δ. Sr enrichment in many electrocatalysts, such as La1-xSrxMO3-δ (M = Cr, Co, Mn, or Co and Fe) and Sm1-xSrxCoO3, has been probed using alternative techniques, including low energy ion scattering, secondary ion mass spectrometry, and X-ray fluorescence-based methods for depth-dependent, element-specific analysis. We highlight a strong connection between cation segregation and electrocatalytic properties, because cation segregation enhances oxygen transport and surface oxygen exchange kinetics. On the other hand, the formation of cation-enriched secondary phases can lead to the blocking of active sites, inhibiting oxygen exchange. With help from density functional theory, the links between cation migration, catalyst stability, and catalytic activity are provided, and the oxygen p-band center relative to the Fermi level can be identified as an activity descriptor. Based on these findings, we discuss strategies to increase a catalyst's activity while maintaining stability to design efficient, cost-effective electrocatalysts.

Correction: Ab initio and empirical defect modeling of LaMnO3±Î´ for solid oxide fuel cell cathodes.

Correction for 'Ab initio and empirical defect modeling of LaMnO3±Î´ for solid oxide fuel cell cathodes' by Yueh-Lin Lee et al., Phys. Chem. Chem. Phys., 2012, 14, 290-302.

Kinetics of Oxygen Surface Exchange on Epitaxial Ruddlesden-Popper Phases and Correlations to First-Principles Descriptors.

Through alignment of theoretical modeling with experimental measurements of oxygen surface exchange kinetics on (001)-oriented La2-xSrxMO4+δ (M = Co, Ni, Cu) thin films, we demonstrate here the capability of the theoretical bulk O 2p-band centers to correlate with oxygen surface-exchange kinetics of the Ruddlesden-Popper oxide (RP214) (001)-oriented thin films. In addition, we demonstrate that the bulk O 2p-band centers can also correlate with the experimental activation energies for bulk oxygen transport and oxygen surface exchange of both the RP214 and the perovskite polycrystalline materials reported in the literature, indicating the effectiveness of the bulk O 2p-band centers in describing the associated energetics and kinetics. We propose that the opposite slopes of the bulk O 2p-band center correlations between the RP214 and the perovskite materials are due to the intrinsic mechanistic differences of their oxygen surface exchange kinetics and bulk anionic transport.

Joint Experimental and Computational 17O and 1H Solid State NMR Study of Ba2In2O4(OH)2 Structure and Dynamics.

A structural characterization of the hydrated form of the brownmillerite-type phase Ba2In2O5, Ba2In2O4(OH)2, is reported using experimental multinuclear NMR spectroscopy and density functional theory (DFT) energy and GIPAW NMR calculations. When the oxygen ions from H2O fill the inherent O vacancies of the brownmillerite structure, one of the water protons remains in the same layer (O3) while the second proton is located in the neighboring layer (O2) in sites with partial occupancies, as previously demonstrated by Jayaraman et al. (Solid State Ionics2004, 170, 25-32) using X-ray and neutron studies. Calculations of possible proton arrangements within the partially occupied layer of Ba2In2O4(OH)2 yield a set of low energy structures; GIPAW NMR calculations on these configurations yield 1H and 17O chemical shifts and peak intensity ratios, which are then used to help assign the experimental MAS NMR spectra. Three distinct 1H resonances in a 2:1:1 ratio are obtained experimentally, the most intense resonance being assigned to the proton in the O3 layer. The two weaker signals are due to O2 layer protons, one set hydrogen bonding to the O3 layer and the other hydrogen bonding alternately toward the O3 and O1 layers. 1H magnetization exchange experiments reveal that all three resonances originate from protons in the same crystallographic phase, the protons exchanging with each other above approximately 150 °C. Three distinct types of oxygen atoms are evident from the DFT GIPAW calculations bare oxygens (O), oxygens directly bonded to a proton (H-donor O), and oxygen ions that are hydrogen bonded to a proton (H-acceptor O). The 17O calculated shifts and quadrupolar parameters are used to assign the experimental spectra, the assignments being confirmed by 1H-17O double resonance experiments.

Activity and stability trends of perovskite oxides for oxygen evolution catalysis at neutral pH.

Perovskite oxides (ABO3) have been studied extensively to promote the kinetics of the oxygen evolution reaction (OER) in alkaline electrolytes. However, developing highly active catalysts for OER at near-neutral pH is desirable for many photoelectrochemical/electrochemical devices. In this paper, we systematically studied the activity and stability of well-known perovskite oxides for OER at pH 7. Previous activity descriptors established for perovskite oxides at pH 13, such as having an eg occupancy close to unity or having an O p-band center close to Fermi level, were shown to scale with OER activity at pH 7. Stability was a greater challenge at pH 7 than at pH 13, where two different modes of instability were identified from combined transmission electron microscopy and density functional theory analyses. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization under all overpotentials examined at pH 7, while those with O p-band far from Fermi level were stable under low OER current/potential but became unstable at high current/potential accompanied by leaching of B-site atoms. Therefore, efforts are needed to enhance the activity and stability of perovskites against A-site or B-site loss if used at neutral pH.

Ab initio GGA+U study of oxygen evolution and oxygen reduction electrocatalysis on the (001) surfaces of lanthanum transition metal perovskites LaBO3 (B = Cr, Mn, Fe, Co and Ni).

In this work, we performed density functional theory (DFT) calculations with inclusion of Hubbard U corrections for the transition metal d-electrons, to investigate stability and electrocatalytic activities of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) for the ABO3 (A = La; B = Cr, Mn, Fe, Co, and Ni) (001) surfaces. We showed surface binding energies of relevant ORR/OER species are coupled strongly to surface polarity and local oxidation states, giving large (∼1 eV scale per adsorbate) differences in binding between (001) AO and BO2 surfaces, where the more oxidized BO2 bare surfaces in general exhibit weak coverage dependence, while the more reduced AO bare surfaces of the LaCrO3, LaMnO3, and LaFeO3 perovskites with lower d-electron filling show strong/moderate coverage dependences. We then predicted that surface coverage can play a key role in determining surface stability, and when coverage effects are included the AO and BO2(001) surfaces have either similar stability or the AO surface is more stable, as found for 1 monolayer HO* covered AO surfaces of LaCrO3 and LaFeO3 under ORR conditions and 1 monolayer O* covered LaNiO3 AO surface under OER conditions. For the (001) AO surfaces with strong coverage dependent surface adsorption, we predicted a decrease in ORR overpotential of 1-2 V with proper treatment of coverage effects as compared to those of the bare surface simulations. Our results indicated that the GGA+U method and proper treatment of coverage effects more accurately predict ORR and OER overpotentials relative to experimental values as compared to the GGA method and bare surfaces. The overall ORR activity trends vs. the LaBO3 series were predicted to be Co > Mn ≈ Ni > Fe > Cr.

Joint experimental and computational 17O solid state NMR study of Brownmillerite Ba2In2O5.

Structural characterization of Brownmillerite Ba2In2O5 was achieved by an approach combining experimental solid-state NMR spectroscopy, density functional theory (DFT) energetics, and GIPAW NMR calculations. While in the previous study of Ba2In2O5 by Adler et al. (S. B. Adler, J. A. Reimer, J. Baltisberger and U. Werner, J. Am. Chem. Soc., 1994, 116, 675-681), three oxygen resonances were observed in the (17)O NMR spectra and assigned to the three crystallographically unique O sites, the present high resolution (17)O NMR measurements under magic angle spinning (MAS) find only two resonances. The resonances have been assigned using first principles (17)O GIPAW NMR calculations to the combination of the O ions connecting the InO4 tetrahedra and the O ions in equatorial sites in octahedral InO6 coordination, and to the axial O ions linking the four- and six-fold coordinated In(3+) ions. Possible structural disorder was investigated in two ways: firstly, by inclusion of the high-energy structure also previously studied by Mohn et al. (C. E. Mohn, N. L. Allan, C. L. Freeman, P. Ravindran and S. Stølen, J. Solid State Chem., 2005, 178, 346-355), where the structural O vacancies are stacked rather than staggered as in Brownmillerite and, secondly, by exploring structures derived from the ground-state structure but with randomly perturbed atomic positions. There is no noticeable NMR evidence for any substantial occupancy of the high-energy structure at room temperature.

Anomalous Interface and Surface Strontium Segregation in (La1-ySry)2CoO4±Î´/La1-xSrxCoO3-δ Heterostructured Thin Films.

Heterostructured oxides have shown unusual electrochemical properties including enhanced catalytic activity, ion transport, and stability. In particular, it has been shown recently that the activity of oxygen electrocatalysis on the Ruddlesden-Popper/perovskite (La1-ySry)2CoO4±Î´/La1-xSrxCoO3-δ heterostructure is remarkably enhanced relative to the Ruddlesden-Popper and perovskite constituents. Here we report the first atomic-scale structure and composition of (La1-ySry)2CoO4±Î´/La1-xSrxCoO3-δ grown on SrTiO3. We observe anomalous strontium segregation from the perovskite to the interface and the Ruddlesden-Popper phase using direct X-ray methods as well as with ab initio calculations. Such Sr segregation occurred during the film growth, and no significant changes were found upon subsequent annealing in O2. Our findings provide insights into the design of highly active catalysts for oxygen electrocatalysis.

Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution.

The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln0.5Ba0.5)CoO(3-δ) (Ln=Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidation in alkaline solution. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band centre neither too close nor too far from the Fermi level, which is computed from ab initio studies.