Electronic structure and transport properties of coupled CdS/ZnSe quantum dots.

Electronic structure and transport characteristics of coupled CdS and ZnSe quantum dots are studied using density functional theory and non equilibrium Greens function method respectively. Our investigations show that in these novel coupled dots, the Frontier occupied and unoccupied molecular orbitals are spatially located in two different parts, thereby indicating the possibility of asymmetry in electronic transport. We have calculated electronic transport through the coupled quantum dot by varying the coupling strength between the individual quantum dots in the limits of weak and strong coupling. Calculations reveal asymmetric current vs voltage curves in both the limits indicating the rectifying properties of the coupled quantum dots. Additionally we discuss the possibility to tune the switching behavior of the coupled dots by different gate geometries.

Interpretation and Automatic Generation of Fermi-Orbital Descriptors.

We present an interpretation of Fermi-orbital descriptors (FODs) and argue that these descriptors carry chemical bonding information. We show that a bond order derived from these FODs agrees well with reference values, and highlight that optimized FOD positions used within the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method correspond to expectations from Linnett's double-quartet theory, which is an extension of Lewis theory. This observation is independent of the underlying exchange-correlation functional, which is shown using the local spin density approximation, the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA), and the strongly constrained and appropriately normed meta-GGA. To make FOD positions generally accessible, we propose and discuss four independent methods for the generation of Fermi-orbital descriptors, their implementation as well as their advantages and drawbacks. In particular, we introduce a re-implementation of the electron force field, an approach based on the centers of mass of orbital densities, a Monte Carlo-based algorithm, and a method based on Lewis-like bonding information. All results are summarized with respect to future developments of FLO-SIC and related methods. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.

Magnetic Signatures of Hydroxyl- and Water-Terminated Neutral and Tetra-Anionic Mn12 -Acetate.

We investigate the energetics and magnetic signatures of the parent molecular magnet Mn12 -Acetate [Mn12 O12 (COOR)16 (H2 O)4 ] and a chemically decomposed version of this structure, in which the four water molecules are converted to hydroxyl groups and hydrogen molecules. We determine electron addition and water decomposition energetics for this water-containing molecule using density-functional methods and include the recent Fermi-Löwdin-Orbital self-interaction correction. We find that it only costs 0.32 eV to add four electrons to the parent molecule. Furthermore, due to the strong Coulomb attractions between hydroxyl anions and the Mn cations, the energy cost for breaking the four coordinating water molecules into four coordinating hydroxyls and two hydrogen molecules is decreased in the tetra-anionic structure relative to the neutral structure. We calculate magnetic anisotropy barriers for the neutral molecule and the dehydrogenated tetra-anion and show that large changes in the magnetic anisotropy arise the strong attraction between the hydroxyl anions and four of the crown Mn cations. We suggest that the large changes in magnetic signals associated with the [Mn12 O12 (COOR)16 (HOH)4 ] to [Mn12 O12 (COOR)16 (OH- )4 + 2H2 ] decomposition could provide a nondestructive spectroscopic method for learning about water decomposition mechanisms in a class of realizable model catalytic systems that have been synthesized recently. © 2019 Wiley Periodicals, Inc.

Stretched or noded orbital densities and self-interaction correction in density functional theory.

Semilocal approximations to the density functional for the exchange-correlation energy of a many-electron system necessarily fail for lobed one-electron densities, including not only the familiar stretched densities but also the less familiar but closely related noded ones. The Perdew-Zunger (PZ) self-interaction correction (SIC) to a semilocal approximation makes that approximation exact for all one-electron ground- or excited-state densities and accurate for stretched bonds. When the minimization of the PZ total energy is made over real localized orbitals, the orbital densities can be noded, leading to energy errors in many-electron systems. Minimization over complex localized orbitals yields nodeless orbital densities, which reduce but typically do not eliminate the SIC errors of atomization energies. Other errors of PZ SIC remain, attributable to the loss of the exact constraints and appropriate norms that the semilocal approximations satisfy, suggesting the need for a generalized SIC. These conclusions are supported by calculations for one-electron densities and for many-electron molecules. While PZ SIC raises and improves the energy barriers of standard generalized gradient approximations (GGAs) and meta-GGAs, it reduces and often worsens the atomization energies of molecules. Thus, PZ SIC raises the energy more as the nodality of the valence localized orbitals increases from atoms to molecules to transition states. PZ SIC is applied here, in particular, to the strongly constrained and appropriately normed (SCAN) meta-GGA, for which the correlation part is already self-interaction-free. This property makes SCAN a natural first candidate for a generalized SIC.

Analytic atomic gradients in the fermi-löwdin orbital self-interaction correction.

We derived, implemented, and thoroughly tested the complete analytic expression for atomic forces, consisting of the Hellmann-Feynman term and the Pulay correction, for the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method. Analytic forces are shown to be numerically accurate through an extensive comparison to forces obtained from finite differences. Using the analytic forces, equilibrium structures for a small set of molecules were obtained. This work opens the possibility of routine self-interaction free geometrical relaxations of molecules using the FLO-SIC method. © 2018 Wiley Periodicals, Inc.

Fermi-Löwdin orbital self-interaction corrected density functional theory: Ionization potentials and enthalpies of formation.

The Fermi-Löwdin orbital self-interaction correction (FLO-SIC) methodology is applied to atoms and molecules from the standard G2-1 test set. For the first time FLO-SIC results for the GGA-type PBE functional are presented. In addition, examples where FLO-SIC like any proper SIC provides qualitative improvements compared to standard DFT functionals are discussed in detail: the dissociation limit for H 2 + , the step-wise linearity behavior for fractional occupation, as well as the significant reduction of the error of static polarizabilities. Further, ionization potentials and enthalpies of formation obtained by means of the FLO-SIC DFT method are compared to other SIC variants and experimental values. The self-interaction correction gives significant improvements if used with the LDA functional but shows worse performance in case of enthalpies of formation if the PBE-GGA functional is used. The errors are analyzed and the importance of the overbinding of hydrogen is discussed. © 2018 Wiley Periodicals, Inc.

Electronic structure, transport, and collective effects in molecular layered systems.

The great potential of organic heterostructures for organic device applications is exemplified by the targeted engineering of the electronic properties of phthalocyanine-based systems. The transport properties of two different phthalocyanine systems, a pure copper phthalocyanine (CoPc) and a flourinated copper phthalocyanine-manganese phthalocyanine (F16CoPc/MnPc) heterostructure, are investigated by means of density functional theory (DFT) and the non-equilibrium Green's function (NEGF) approach. Furthermore, a master-equation-based approach is used to include electronic correlations beyond the mean-field-type approximation of DFT. We describe the essential theoretical tools to obtain the parameters needed for the master equation from DFT results. Finally, an interacting molecular monolayer is considered within a master-equation approach.

Self-consistent self-interaction corrected density functional theory calculations for atoms using Fermi-Löwdin orbitals: Optimized Fermi-orbital descriptors for Li-Kr.

In the Fermi-Löwdin orbital method for implementing self-interaction corrections (FLO-SIC) in density functional theory (DFT), the local orbitals used to make the corrections are generated in a unitary-invariant scheme via the choice of the Fermi orbital descriptors (FODs). These are M positions in 3-d space (for an M-electron system) that can be loosely thought of as classical electron positions. The orbitals that minimize the DFT energy including the SIC are obtained by finding optimal positions for the FODs. In this paper, we present optimized FODs for the atoms from Li-Kr obtained using an unbiased search method and self-consistent FLO-SIC calculations. The FOD arrangements display a clear shell structure that reflects the principal quantum numbers of the orbitals. We describe trends in the FOD arrangements as a function of atomic number. FLO-SIC total energies for the atoms are presented and are shown to be in close agreement with the results of previous SIC calculations that imposed explicit constraints to determine the optimal local orbitals, suggesting that FLO-SIC yields the same solutions for atoms as these computationally demanding earlier methods, without invoking the constraints.

Symmetry Breaking within Fermi-Löwdin Orbital Self-Interaction Corrected Density Functional Theory.

Fermi-Löwdin orbital self-interaction corrected density functional theory (FLO-SIC DFT) is applied to C3H5, NO3-, O3, and CH3. In general our results indicate that FLO-SIC does favor symmetric setups for molecules with nontrivial chemical bonding. Further we discuss two types of possible symmetry breaking. In the case of O3 a ground state density that breaks symmetry can be found for the symmetric molecular geometry that may be caused by insufficient treatment of correlation energy. The CH3 radical presents a second type of symmetry breaking were the lowest energy geometry becomes distorted. The latter highlights the importance of further development of approximate DFT functionals as well as further extensions of the FLO-SIC method to overcome such nonphysical artifacts.

Charge transfer from and to manganese phthalocyanine: bulk materials and interfaces.

Manganese phthalocyanine (MnPc) is a member of the family of transition-metal phthalocyanines, which combines interesting electronic behavior in the fields of organic and molecular electronics with local magnetic moments. MnPc is characterized by hybrid states between the Mn 3d orbitals and the π orbitals of the ligand very close to the Fermi level. This causes particular physical properties, different from those of the other phthalocyanines, such as a rather small ionization potential, a small band gap and a large electron affinity. These can be exploited to prepare particular compounds and interfaces with appropriate partners, which are characterized by a charge transfer from or to MnPc. We summarize recent spectroscopic and theoretical results that have been achieved in this regard.

Antibiotic mixture effects on growth of the leaf-shredding stream detritivore Gammarus fossarum.

Pharmaceuticals contribute greatly to human and animal health. Given their specific biological targets, pharmaceuticals pose a significant environmental risk by affecting organisms and ecosystem processes, including leaf-litter decomposition. Although litter decomposition is a central process in forest streams, the consequences of exposure to pharmaceuticals remain poorly known. The present study assessed the impact of antibiotics as an important class of pharmaceuticals on the growth of the leaf-shredding amphipod Gammarus fossarum over 24 days. Exposure scenarios involved an antibiotic mixture (i.e. sulfamethoxazole, trimethoprim, erythromycin-H2O, roxithromycin, clarithromycin) at 0, 2 and 200 µg/L to assess impacts resulting from exposure to both water and food. The antibiotics had no effect on either leaf-associated fungal biomass or bacterial abundance. However, modification of leaf quality (e.g. through shifts in leaf-associated microbial communities) may have triggered faster growth of gammarids (assessed in terms of body mass gain) at the low antibiotic concentration relative to the control. At 200 µg/L, however, gammarid growth was not stimulated. This outcome might be due to a modified ability of the gut microflora to assimilate nutrients and carbon. Furthermore, the observed lack of increases in the diameter of the gammarids' peduncles, despite an increase in gammarid mass, suggests antibiotic-induced effects in the moulting cycle. Although the processes responsible for the observed effects have not yet been identified, these results suggest a potential role of food-quality, gammarid gut microflora and alteration in the moulting cycle in mediating impacts of antibiotics on these detritivores and the leaf decomposition process in streams.

Acute Toxicity and Environmental Risks of Five Veterinary Pharmaceuticals for Aquatic Macroinvertebrates.

Due to the high use of antibiotics and antiparasitics for the treatment of livestock, there is concern about the potential impacts of the release of these compounds into freshwater ecosystems. In this context, the present study quantified the acute toxicity of two antibiotics (sulfadiazine and sulfadimidine), and three antiparasitic agents (flubendazole, fenbendazole, ivermectin) for nine freshwater invertebrate species. These experiments revealed a low degree of toxicity for the sulfonamide antibiotics, with limited implications in the survival of all test species at the highest test concentrations (50 and 100 mg/L). In contrast, all three antiparasitic agents indicated on the basis of their acute toxicity risks for the aquatic environment. Moreover, chronic toxicity data from the literature for antiparasitics, including effects on reproduction in daphnids, support the concern about the integrity of aquatic ecosystems posed by releases of these compounds. Thus, these pharmaceuticals warrant further careful consideration by environmental risk managers.

Magnetic superexchange interactions: trinuclear bis(oxamidato) versus bis(oxamato) type complexes.

The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me , Et , (n)Pr ) in good yields. Treatment of with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [(n)Bu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [(n)Bu4N]2[M(opboR2)] (M = Ni, R = Me , Et , (n)Pr ; M = Cu, R = Me , Et , (n)Pr ). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of , novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me , Et , (n)Pr ) could be obtained. Compounds have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of and have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted and (1%) in the host lattice of and (99%) (@ and @), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)](2-) and [Cu(opbo(n)Pr2)](2-) complex fragments of and , respectively, could be determined. Additionally, as a single crystal ENDOR measurement of @ revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of were studied by susceptibility measurements versus temperature to give J values varying from -96 cm(-1) () over -104 cm(-1) () to -132 cm(-1) (). These three trinuclear Cu(II)-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of and , the geometries of the terminal [Cu(pmdta)](2+) fragments of determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.

A gate controlled molecular switch based on picene-F4TCNQ charge-transfer material.

We show that the recently synthesized charge-transfer material picene-F4TCNQ can be used as a gate-voltage controlled molecular switch. The picene-F4TCNQ system is compared with the extensively characterized anthraquinone-based molecular system, which is known to exhibit large switching ratios due to quantum interference effects. In the case of picene-F4TCNQ we find switching ratios larger by one order of magnitude. Further, our calculations reveal that the picene-F4TCNQ system resembles remarkably well the I-V characteristics of a classical diode. The reverse-bias current of this molecular diode can be increased two orders of magnitude by an external gate voltage. Based on density-functional theory calculations we show that the hybrid states formed by the picene-F4TCNQ system play the key role in determining transport properties. We further conclude that the tuning of quantum transport properties through hybrid states is a general concept which opens a new route towards functional materials for molecular electronics.

Optical and magneto-optical properties of metal phthalocyanine and metal porphyrin thin films.

The optical constants together with the magneto-optical Voigt constants of several phthalocyanine (Pc) and methoxy functionalized tetraphenylporphyrin (TMPP) thin films prepared on silicon substrates are presented. The materials investigated are MePc with Me = Fe, Co, Ni, Cu, Zn and MeTMPP with Me = Cu, Ni. We also compared our results to the metal-free H2Pc, H2TPP and H2TMPP. The experimental results will be supported by electronic structure calculations based on density functional theory (DFT) and interpreted using the perimeter model initially proposed by Platt. The model allows for qualitative understanding of the forbidden character of transitions in planar, aromatic molecules, and is able to qualify differences between Pc and TMPP type materials.

Phthalocyanine dimers in a blend: spectroscopic and theoretical studies of MnPc(δ +)/F(16)CoPc(δ -).

We have prepared mixed phthalocyanine films out of MnPc and F(16)CoPc, which were characterized by means of photoemission spectroscopy and electron energy-loss spectroscopy. Our data reveal the formation of MnPc/F(16)CoPc charge transfer dimers in analogy to the related heterojunction. The electronic excitation spectrum of these blends is characterized by a new low energy excitation at 0.6 eV. Density functional theory calculations show that the new signal is caused by a strong absorption between the states of the interface induced two level system.

Binuclear nickel complexes with an edge sharing bis(square-pyramidal) N3Ni(µ-S2)NiN3 core: synthesis, characterization, crystal structure and magnetic properties.

The synthesis of the novel macrocyclic octadentate amino-thiophenolate ligand H(2)L2 (3,7,11,19,23,27-hexaaza-33,34-dithiol-15,31-di(tert-butyl)-tricyclo[27,3,1(13.17)]-tetratriaconta-1(32),13,15,17(34),29,30-hexane) and its ability to support binuclear nickel(II) complexes with dithiolato-bridged square-pyramidal Ni(II) ions are reported. H(2)L2 is obtained as the hexahydrobromide salt from a Schiff-base condensation reaction between 1,2-bis(4-tert-butyl-2,6-diformylphenylthio)ethane and bis(3-aminopropyl)amine followed by two successive reductions with NaBH(4) and Na/NH(3). The ligand forms a green, paramagnetic, binuclear nickel(II) complex dication [Ni(II)(2)L2](2+), which can be isolated as a ClO(4)(-) (4) or BPh(4)(-) salt (5). The binuclear nickel(II) complex contains a central N(3)Ni(µ-S)(2)NiN(3) core with two square-pyramidal coordinated Ni(II) ions. The [Ni(2)L2](2+) dication does not bind further coligands, in striking contrast to the behaviour of the parent [Ni(2)L1](2+) dication supported by the smaller (L1)(2-) macrocycle (containing diethylenetriamine in place of the dipropylenetriamine units) which readily binds a variety of other coligands (L') to form bisoctahedral [Ni(2)L1(L')](+) structures. The unusual behaviour of 4 relates to two different N configurations which leads to a steric shielding of the third bridging position by the CH(2)-groups of the dipropylenetriamine chains. An analysis of the temperature-dependent magnetic susceptibility data of 5 reveals the presence of a weak antiferromagnetic exchange interaction between the spins of the nickel(II) ions with a value for the magnetic exchange coupling constant J of -23.5 cm(-1) (H = -2JS(1)S(2)). These results are further substantiated by DFT calculations.

Stabilization of hypophosphite in the binding pocket of a dinuclear macrocyclic complex: synthesis, structure, and properties of [Ni(2)L(µ-O(2)PH(2))]BPh(4) (L = N(6)S(2) donor ligand).

The dinickel(II) complex [Ni2L(ClO4)]ClO4 (1), where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolate ligand, reacts with [nBu4N]H2PO2 to form the hypophosphito-bridged complex [Ni2L(µ-O2PH2)](+), which can be isolated as an air-stable perchlorate [Ni2L(µ-O2PH2)]ClO4 (2) or tetraphenylborate [Ni2L(µ-O2PH2)]BPh4 (3) salt. 3·MeCN crystallizes in the triclinic space group P1̅. The bisoctahedral [Ni2L(µ-O2PH2)](+) cation has a N3Ni(µ1,3-O2PH2)(µ-S)2NiN3 core structure with the hypophosphito ligand attached to the two Ni(II) ions in a µ1,3-bridging mode. The hypophosphito ligand is readily replaced by carboxylates, in agreement with a higher affinity of the [Ni2L](2+) dication for more basic oxoanions. Treatment of [Ni2L(µ-O2PH2)]ClO4 with H2O2 or MCPBA results in the oxidation of the bridging thiolato to sulfonato groups. The hypophosphito group is not oxidized under these conditions due to the steric protection offered by the supporting ligand. An analysis of the temperature-dependent magnetic susceptibility data for 3 reveals the presence of ferromagnetic exchange interactions between the Ni(ii) (S = 1) ions with a value for the magnetic exchange coupling constant J of +22 cm(-1) (H = -2JS1S2). These results are additionally supported by DFT (density functional theory) calculations.

Hybrid states and charge transfer at a phthalocyanine heterojunction: MnPc(δ+)/F16CoPc(δ-).

Using photoelectron spectroscopy we demonstrate charge transfer at an interface between two well-known transition metal phthalocyanines, MnPc and F16CoPc, resulting in charged MnPc(δ+) and F16CoPc(δ-) species. Moreover, the transferred charge is substantially confined to the two transition metal centers. Density functional theory calculations reveal that a hybrid state is formed between the two types of phthalocyanines, which causes this charge transfer. For the hybrid state the Mn 3d(xz) interacts with the Co 3d(z2) orbital leading to a two-level system. As only the lower of the two hybrid states is occupied, the charge is directly transferred to the Co 3d(z2) orbital.

An interplay between the spin density distribution and magnetic superexchange interactions: a case study of mononuclear [(n)Bu4N]2[Cu(opooMe)] and novel asymmetric trinuclear [Cu3(opooMe)(pmdta)2](NO3)2·3MeCN.

Treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Et(2), 1) with 5/6 equivalent of MeNH(2) in abs. EtOH results in the exclusive formation of the ethyl ester of o-phenylene(N'-methyl oxamide)(oxamic acid) (opooH(3)EtMe, 2) in ca. 50% yield. Treatment of 2 with four equivalents of [Me(4)N]OH followed by the addition of Cu(ClO(4))(2)·6H(2)O gave [Me(4)N](2)[Cu(opooMe)]·H(2)O (3A) in ca. 80% yield. As 3A appears to be a hygroscopic solid, the related [(n)Bu(4)N](+) salts [(n)Bu(4)N](2)[M(opooMe)]·H(2)O (M = Cu (3B), Ni (4)) have been synthesized. By addition of two equivalents of [Cu(pmdta)(NO(3))(2)] to a MeCN solution of 3B the novel asymmetric trinuclear complex [Cu(3)(opooMe)(pmdta)(2)](NO(3))(2) (5) could be obtained in ca. 90% yield. Compounds 2, 3A, 3B, 4 and 5 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 3A in the form of [Me(4)N](2)[Cu(opooMe)]·MeOH (3A'), 3B in the form of [(n)Bu(4)N](2)[Cu(opooMe)] (3B'), 4 in the form of [(n)Bu(4)N](2)[Ni(opooMe)]·1.25H(2)O (4') and 5 in the form of [Cu(3)(opooMe)(pmdta)(2)] (NO(3))(2)·3MeCN (5'), respectively, have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 3B (1%) in the host lattice of 4 (99%) in the form of single crystals have been made available, allowing single crystal EPR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine interaction. Out of these studies the spin density distribution of the [Cu(opooMe)](2-) complex fragment could be determined. The magnetic properties of 5 were studied by susceptibility measurements versus temperature. An intramolecular J parameter of -65 cm(-1) has been obtained, unexpectedly, as 5 should possess two different J values due to its two different spacers between the adjacent Cu(II) ions, namely an oxamate (C(2)NO(3)) and an oxamidate (C(2)N(2)O(2)) fragment. This unexpected result is explained by a summarizing discussion of the experimentally obtained EPR results (spin density distribution) of 3B, the geometries of the terminal [Cu(pmdta)](2+) fragments of 5 determined by X-ray crystallographic studies and accompanying quantum chemical calculations of the spin density distribution of the mononuclear [Cu(opooMe)](2-) and of the magnetic exchange interactions of trinuclear [Cu(3)(opooMe)(pmdta)(2)](2+) complex fragments.