The electronic transport coefficients of three Earth-abundant metal oxides Cu2O, CuO, and NiO were investigated using hybrid density functional theory (DFT). Hybrid DFT methods combined with local ...Gaussian-type basis sets enabled band structure studies on both non-magnetic and magnetic p-type metal oxides without empirical corrections. The CRYSTAL code was used for obtaining the wavefunction, and the transport properties were calculated with two different methodologies to benchmark their accuracy: a numerical approach as implemented in the BoltzTraP code and an analytical approach recently implemented in CRYSTAL17. Both computational methods produce identical results in good agreement with experimental measurements of the Seebeck coefficient. The predicted electrical conductivities are overestimated, owing likely to the used approximation of a constant electronic relaxation time in the calculations, as explicit electron scattering is neglected and relaxation time is considered only as a free parameter. The obtained results enable us to critically review and complement the available theoretical and experimental literature on the studied p-type thermoelectric metal oxide materials.
We investigated crystalline ZnO:hydroquinone (HQ) superlattices grown layer-by-layer by the combined atomic/molecular layer deposition (ALD/MLD) technique; such ALD/MLD layer-engineered ...inorganic–organic thin films form a fundamentally new category of functional coherent hybrid materials that cannot be prepared by any other existing technique. Using quantum chemical methods, we derive atomic-level structural models for the ZnO:HQ superlattices and investigate their structural, spectroscopic, and electronic properties. By comparing the theoretical results with our experimental data we provide a detailed interpretation of experimentally measured infrared spectra, proving the presence of organic interfaces within the crystalline ZnO:HQ superlattices. We moreover show how the band structure of the hybrid material can be tailored by simple and experimentally feasible modifications of the organic constituent. The guidelines for the band-structure engineering of ZnO:HQ superlattices should be valuable for the systematic enhancement and exploitation of the functional properties of ALD/MLD-grown inorganic–organic superlattices and nanolaminates in general.
After decades of waiting, computational chemistry for the masses is finally here. Our brief review on free and open source software (FOSS) packages points out the existence of software offering a ...wide range of functionality, all the way from approximate semiempirical calculations with tight‐binding density functional theory to sophisticated ab initio wave function methods such as coupled‐cluster theory, covering both molecular and solid‐state systems. Combined with the remarkable increase in the computing power of personal devices, which now rivals that of the fastest supercomputers in the world in the 1990s, we demonstrate that a decentralized model for teaching computational chemistry is now possible thanks to FOSS packages, enabling students to perform reasonable modeling on their own computing devices in the bring your own device (BYOD) scheme. FOSS software can be made trivially simple to install and keep up to date, eliminating the need for departmental support, and also enables comprehensive teaching strategies, as various algorithms' actual implementations can be used in teaching. We exemplify what kinds of calculations are feasible with four FOSS electronic structure programs, assuming only extremely modest computational resources, to illustrate how FOSS packages enable decentralized approaches to computational chemistry education within the BYOD scheme. FOSS also has further benefits driving its adoption: the open access to the source code of FOSS packages democratizes the science of computational chemistry, and FOSS packages can be used without limitation also beyond education, in academic and industrial applications, for example.
This article is categorized under:
Software > Quantum Chemistry
We show that quantum chemical calculations can be routinely performed with free and open source software (FOSS) on commodity hardware, enabling the bring your own device (BYOD) paradigm for computational chemistry education.
UO2F2 abstracts F− anions from TlF in liquid ammonia solution and the compound Tl2(NH3)6{UO2F2(NH3)}2(μ‐F)2 is formed. The compound has been characterized by single crystal X‐ray diffraction, Raman ...spectroscopy and quantum‐chemical calculations for the solid state. Quantum‐chemical investigation of the {UO2F2(NH3)}2(μ‐F)22− anion showed that the U−(μ‐F)−U σ‐3c‐4e‐bond is essentially ionic. The Tl2(NH3)62+ cation shows a thallophilic Tl⋅⋅⋅Tl interaction. Fluoride ion affinities (FIAs) were calculated for different UO22+ species UO2Fx2−x and UO2Fx(NH3)5−x2−x with x=0 to 4.
Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed‐shell molecular hexafluorides MF6 (M=S, Se, Te, Xe, Mo, W, U). First, ...the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all‐electron basis sets and explicitly considering the influence of spin‐orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF6 molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF6 molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF6 molecule.
The anharmonic IR spectra of known and unknown closed‐shell molecular hexafluorides MF6 (with M=Cr, Mo, W, U, S, Se, Te, Po, Xe, Rn) were calculated at the CCSD(T)/cc‐pVTZ(‐PP) level of theory. The unknown NdF6 molecule was predicted to be stable on the potential energy surface and its chemical bonds were investigated in comparison with those of UF6 by intrinsic bond orbital analysis.
-metal oxides play a crucial role in numerous technological applications and show a great variety of magnetic properties. We have systematically investigated the structural properties, magnetic ...ground states, and fundamental electronic properties of 100 binary
-metal oxides using hybrid density functional methods and localized basis sets composed of Gaussian-type functions. The calculated properties are compared with experimental information in all cases where experimental data are available. The used PBE0 hybrid density functional method describes the structural properties of the studied
-metal oxides well, except in the case of molecular oxides with weak intermolecular forces between the molecular units. Empirical D3 dispersion correction does not improve the structural description of the molecular oxides. We provide a database of optimized geometries and magnetic ground states to facilitate future studies on the more complex properties of the binary
-metal oxides.
Binary zinc(II) oxide (ZnO) and copper(II) oxide (CuO) are used in a number of applications, including optoelectronic and semiconductor applications. However, no crystal structures have been reported ...for ternary Cu-Zn-O oxides. In that context, we investigated the structural characteristics and thermodynamics of CuxZnyOz ternary oxides to map their experimental feasibility. We combined evolutionary crystal structure prediction and quantum chemical methods to investigate potential CuxZnyOz ternary oxides. The USPEX algorithm and density functional theory were used to screen over 4000 crystal structures with different stoichiometries. When comparing compositions with non-magnetic CuI ions, magnetic CuII ions, and mixed CuI-CuII compositions, the magnetic Cu2Zn2O4 system is thermodynamically the most favorable. At ambient pressures, the thermodynamically most favorable ternary crystal structure is still 2.8 kJ/mol per atom higher in Gibbs free energy compared to experimentally known binary phases. The results suggest that thermodynamics of the hypothetical CuxZnyOz ternary oxides should also be evaluated at high pressures. The predicted ternary materials are indirect band gap semiconductors.
Half-Heusler alloys are thermoelectric materials that enable direct conversion of waste heat to electricity. A systematic study of these alloys has never been attempted using local Gaussian type ...orbitals (GTOs) and hybrid density functional theory methods within a periodic approach. In this work, we study the thermoelectric properties of TiMSn (M = Ni, Pd, and Pt) alloys with space group F4̅3m using the CRYSTAL code. We, first, set benchmarks for TiNiSn by comparing our data to existing literature values of Seebeck coefficient, power-factor, and thermoelectric figure-of-merit. Our results agree well. We, then, extend these calculations to TiPdSn and TiPtSn, for which consistent previous data are limited. Our computations show that all TiMSn (M = Ni, Pd, and Pt) alloys prefer p-type carriers and exhibit a figure-of-merit of ≈1 at a chosen carrier concentration and temperature. In addition, we aim to explain the low band-gap of TiNiSn by modeling defects in the pure system. Our defect model proves to have a smaller band-gap, and its power-factor is found to be almost twice of the pure TiNiSn.
The phonon properties and thermodynamics of four crystalline cellulose allomorphs, Iα, Iβ, II, and III1, have been investigated using dispersion-corrected density functional theory (DFT). In line ...with experimental findings, the free energy differences between the studied cellulose allomorphs are small, less than 1 kJ/mol per atom. The calculated specific heat at constant volume (Cv) has been compared with the available experimental data in the temperature range 10–300 K. Quasiharmonic approximation has been employed to study thermodynamics and specific heat at constant pressure (Cp). For the studied temperature range of 10–400 K, the specific heat of all cellulose allomorphs shows very similar behavior. The calculated and experimental specific heat agree well at low temperatures below 100 K, but the deviation between theory and experiment increases with temperature. This may be due to increasing phonon anharmonicity as the temperature increases.
Compounds containing the dioxychloronium cation, ClO2+, were obtained from reactions of ClF3 with various oxides such as TiO2, MoO3, Re2O7, SnO, P2O5, As2O5, and Nb metal, as the latter contained ...oxide as an impurity. Partial hydrolysis of ClF2IrF6 led to the formation of ClO2IrF6. The crystal structures of the compounds were determined by single‐crystal X‐ray diffraction, which showed that depending on the starting material ClO2+ salts with the fluoridometallate anions TiF3/2F3/12−, Nb3F16−, IrF6−, SnF2/2F4/1− PF6−, and AsF6−, or with the oxidofluoridometallate anions Mo3O3F13− and Re3O6F10−, were obtained. Bent ClO2+ cations with short Cl ⋅ ⋅ ⋅ μ−F contacts of surrounding F atoms of the anions with the Cl atom are present in the crystal structures, leading to coordination numbers of 2+4 or 2+6 for the Cl atom. Various structural motifs are observed, which range from molecular, columnar, ladder‐like, to layer and framework structures. The salts were furthermore characterized by Raman spectroscopy and solid‐state quantum‐chemical calculations. Covalent Cl−O bonds and ionic Cl ⋅ ⋅ ⋅ μ−F interactions are indicated by the calculations.
The reaction of ClF3 with oxides (TiO2, MoO3, Re2O7, SnO, P2O5, As2O5) leads to the formation of ClO2+ salts with fluoridometallate or oxidofluoridometallate anions. Such ClO2+ salts also form by hydrolysis of ClF2IrF6, or when ClF3 reacts with metal powders (Nb) that contain oxygen impurities. The crystal structures of the investigated compounds range from molecular, over columnar or ladder‐like, to layer and also framework structures.
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