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We investigate the accuracy of two-component Douglas-Kroll-Hess (DKH) methods in calculations of the nuclear volume term (≡ lnK(nv)) in the isotope fractionation coefficient. lnK(nv) is a main term in the chemical equilibrium constant for isotope exchange reactions in heavy element. Previous work based on the four-component method reasonably reproduced(More)
Energy fitting schemes based on informatics techniques using hierarchical basis sets with small cardinal numbers were numerically investigated to estimate correlation energies at the complete basis set limits. Numerical validations confirmed that the conventional two-point extrapolation models can be unified into a simple formula with optimal parameters(More)
An algorithm of the accompanying coordinate expansion and recurrence relation (ACE-RR), which is used for the rapid evaluation of the electron repulsion integral (ERI), has been extended to the general-contraction (GC) scheme. The present algorithm, denoted by GC-ACE-RR, is designed for molecular calculations including heavy elements, whose orbitals consist(More)
Accurate quantum-chemical calculations of the excitation energies and the rotatory strengths of dichalcogens R-Ch-Ch-R (Ch = S, Se, Te) were carried out with the symmetry adapted cluster (SAC) and SAC-configuration interaction (CI) methods. A series of straight-chain molecules (dihydrogen dichalcogenide, dimethyl dichalcogenide, and (+)-bis(2-methylbutyl)(More)
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