Relativistic multireference M�ller-Plesset perturbation theory calculations for siliconlike ions

Abstract

Relativistic second-order multireference Møller-Plesset perturbation theory calculations are reported for the ground and low-lying excited states of siliconlike ions, Ar +4 , Ti +8 , Fe +12 , Ni +14 , Kr +22 , and Mo +28 . Multiconfiguration Dirac-Fock self-consistent field wave functions were used as reference functions.

Anharmonic vibrational analysis of water with traditional and explicitly correlated coupled cluster methods

“…91 We plan to explore the basis set convergence of quadruple excitation contributions and the importance of different relativistic terms in the future. Also, we hope to address the adequacy of the second-order perturbation treatment of anharmonic effects via a variational solution of the vibrational Schrödinger equation 92,93 using an accurate explicitly correlated potential energy surface.…”

Energy levels of the 4s24p2 states of germanium and germaniumlike ions

“…In our previous works 24, 25 multireference Mø ller–Plesset (MR‐MP) perturbation theory calculations have been reported for some carbonlike and silliconlike ions. Germaniumlike ions also feature the four valence electrons outside the core and energy levels 3 P 0,1,2 , 1 D 2 , and 1 S 0 arising from the ground ns 2 np 2 configuration.…”

“…Siliconlike ions have a more complicated term structure. We have previously 24 investigated moderately ionized siliconlike ions. The 3 s 2 3 p 2 3 P 0,1,2 fine‐structure components was very well described by the MR‐MP procedure using just the 3 s 2 3 p 2 reference space, but calculated energy separations of singlets 1 D 2 and 1 S 0 were not satisfactory even including 3 s 2 3 p 2 and 3 p 4 reference spaces.…”

“…The 𝒥‐averaged MCDF SCF approximation was our choice for zero approximation for the MR‐MP procedure 24. The 𝒥‐average approximation employs a common set of occupied and virtual radial spinors in MR‐MP energy calculations of fine‐structure components.…”

Solvent effects in four‐component relativistic electronic structure theory based on the reference interaction‐site model

“…Nowadays, the relativistic Hartree-Fock (HF), [2][3][4][5] the density functional theory (DFT), 6,7 Møller-Preset perturbation, [8][9][10] configuration interaction (CI), 11,12 and coupled-cluster (CC) 13 methods have been developed and standardly used. In addition to the HF, DFT, and HF-based single reference methods, multiconfiguration methods, such as the multiconfiguration self-consistent field (MCSCF) method, 14,15 multireference (MR) CI, 16 MR perturbation, [17][18][19] and MR CC 20 methods, were developed and are being used. Recently, the four-component full CI Monte Carlo 21 and density matrix renormalization group 22 were formulated.…”