We report new DFT functionals following the local hybrid approach. In these local hybrid functionals (LHs), a local mixing function (LMF) determines the position-dependent exact-exchange admixture. The suggested new pt-LMFs are based on a Padé form and modify the previously used ratio between von Weizsäcker and Kohn–Sham local kinetic energy densities by different powers of the density to enable flexibly improved approximations to the correct high-density and iso-orbital limits relevant for the innermost core region.

Abstract

In local hybrid functionals (LHs), a local mixing function (LMF) determines the position-dependent exact-exchange admixture. We report new LHs that focus on an improvement of the LMF in the core region while retaining or partly improving upon the high accuracy in the valence region exhibited by the LH20t functional. The suggested new pt-LMFs are based on a Padé form and modify the previously used ratio between von Weizsäcker and Kohn–Sham local kinetic energies by different powers of the density to enable flexibly improved approximations to the correct high-density and iso-orbital limits relevant for the innermost core region. Using TDDFT calculations for a set of K-shell core excitations of second- and third-period systems including accurate state-of-the-art relativistic orbital corrections, the core part of the LMF is optimized, while the valence part is optimized as previously reported for test sets of atomization energies and reaction barriers (Haasler et al., J Chem Theory Comput 2020, 16, 5645). The LHs are completed by a calibration function that minimizes spurious nondynamical correlation effects caused by the gauge ambiguities of exchange-energy densities, as well as by B95c meta-GGA correlation. The resulting LH23pt functional relates to the previous LH20t functional but specifically improves upon the core region.

Abstract

We studied the structural, electronic, phonon spectrum and thermoelectric properties of ternary LuMSb (M = Ni, Pd, Pt) half Heusler compounds by using first principles method. The electronic properties are calculated via energy band structure and density of states by using GGA + U approximation. The calculations reveal that the replacement of Ni with Pd and Pt, energy gap decreases and LuNiSb, LuPdSb are found to have narrow indirect band gaps and exhibit semiconducting nature, while LuPtSb is found to be a gapless semiconductor. Phonon band structure calculations give only positive values of phonon frequency indicating the dynamically stability of these compounds. The thermoelectric properties have been computed using semi-classical Boltzmann transport theory. We found high Seebeck coefficient (S) and high power factor (PF) for LuNiSb and LuPdSb compounds in the whole temperature range. The ZT values of LuNiSb and LuPdSb are high in general and reach a maximum of 0.67 and 0.69 at 450 K, respectively, whereas 0.39 is the maximum ZT value for LuPtSb at the same temperature. These findings propose LuNiSb and LuPdSb compounds as promising materials for thermoelectric applications at room temperature.

The most compact relativistic prolapse-free (RPF) Gaussian basis sets ever seen are developed here for cesium through radon, providing small- (SRPF) and medium-size (MRPF) alternatives. The largest errors of these basis sets are consistent with the expected quality level. Soon, these new basis sets should be applied in electronic structure calculations of larger molecular systems with a lower computational cost.

Abstract

Relativistic adapted Gaussian basis sets of small and medium sizes are presented in this study for all elements from cesium to radon, including some alternative electron configurations. Both basis sets are made free of variational prolapse, being developed by means of a polynomial version of the generator coordinate Dirac–Fock method. In addition, these sets were designed to be promptly used with two popular finite nuclear models, uniform sphere and Gaussian nuclei. The largest basis set errors found with the uniform sphere nucleus are 27.3 and 10.6 mHartree, respectively, for the small- and medium-size sets. The largest basis set errors obtained with the Gaussian nuclear model are smaller, reaching 23.2 and 7.1 mHartree for the small- and medium-size sets, respectively. Soon, these basis sets will be augmented with polarization functions to be properly used in molecular calculations.

Abstract

In this study, we present the results of a search for new stable structures of SrC2$$ {}_2 $$O5$$ {}_5 $$ and BaC2$$ {}_2 $$O5$$ {}_5 $$ in the pressure range of 0–100 GPa based on the density functional theory and crystal structure prediction approaches. We have shown that the recently synthesized pyrocarbonate structure SrC2$$ {}_2 $$O5$$ {}_5 $$-P21/c$$ P{2}_1/c $$ is thermodynamically stable for both SrC2$$ {}_2 $$O5$$ {}_5 $$ and BaC2$$ {}_2 $$O5$$ {}_5 $$. Thus, SrC2$$ {}_2 $$O5$$ {}_5 $$-P21/c$$ P{2}_1/c $$ is stable relative to decomposition reaction above 10 GPa, while the lower-pressure stability limit for BaC2$$ {}_2 $$O5$$ {}_5 $$-P21/c$$ P{2}_1/c $$ is 5 GPa, which is the lowest value for the formation of pyrocarbonates. For SrC2$$ {}_2 $$O5$$ {}_5 $$, the following polymorphic transitions were found with increasing pressure: P21/c→Fdd2$$ P{2}_1/c\to Fdd2 $$ at 40 GPa and 1000 K, Fdd2→C2$$ Fdd2\to C2 $$ at 90 GPa and 1000 K. SrC2$$ {}_2 $$O5$$ {}_5 $$-Fdd2$$ Fdd2 $$ and SrC2$$ {}_2 $$O5$$ {}_5 $$-C2$$ C2 $$ are characterized by the framework and layered structures of [CO4$$ {}_4 $$]4−$$ {}^{4-} $$ tetrahedra, respectively. For BaC2$$ {}_2 $$O5$$ {}_5 $$, with increasing pressure, decomposition of BaC2$$ {}_2 $$O5$$ {}_5 $$-P21/c$$ P{2}_1/c $$ into BaCO3$$ {}_3 $$ and CO2$$ {}_2 $$ is observed at 34 GPa without any polymorphic transitions.

The dielectric function of Ba₂XMoO₆ (X = Zn, Cd) double perovskites consists of real and imaginary parts. The real part shows the polarization and dispersion of light energy and imaginary part shows the absorption of light energy. The graphical figure shows the absorption take in the visible and infrared regions which highest peaks at 4.5 eV. Contrary to absorption the polarizations or dispersion of light energy minimum at this point. At resonance frequency the studied materials are completely polarizations, after slight shift of frequency the polarization drops, and maximum absorption of light energy take place.

Abstract

The double perovskites are become the emerging aspirant to fulfill the demand of energy. Therefore, the optoelectronic, elastic and transport characteristics of Ba₂XMoO₆ (X = Zn, Cd) are addressed systemically. The elastic constants show the mechanical stability. The nature of Ba₂ZnMoO₆ is brittle and Ba₂CdMoO₆ is ductile with large values of Debye temperature covalent bonding. The electronic band structures exhibit band gaps of 2.81 and 2.98 eV, which increase their importance for optoelectronic applications. The absorption of light energy, optical loss, refractive index, polarization of light energy are addressed in the energy range zero to 14 eV. Furthermore, thermoelectric characteristics are computed against chemical potentials at 300, 600, and 900 K. The chemical potential decides the p-type nature, with holes as majority carriers. The increasing temperature increases the power factor and figure of merit. Therefore, the optoelectronic and thermoelectric characteristics reveals the importance of studied DPs for energy applications.