scholarly journals Cluster perturbation theory. I. Theoretical foundation for a coupled cluster target state and ground-state energies

2019 ◽  
Vol 150 (13) ◽  
pp. 134108 ◽  
Author(s):  
Filip Pawłowski ◽  
Jeppe Olsen ◽  
Poul Jørgensen
Keyword(s):  
Perturbation Theory ◽  
Ground State ◽  
Theoretical Foundation ◽  
Coupled Cluster ◽  
Target State ◽  
Cluster Perturbation Theory ◽  
Ground State Energies

Application of multireference linearized coupled-cluster theory to atomic and molecular systems

2018 ◽  
Vol 17 (02) ◽  
pp. 1850016 ◽  
Author(s):  
Jiang Yi ◽  
Feiwu Chen
Keyword(s):  
Ground State ◽  
Basis Sets ◽  
Coupled Cluster ◽  
Vibration Frequencies ◽  
Electron Affinities ◽  
Proton Affinities ◽  
Coupled Cluster Theory ◽  
Molecular Systems ◽  
Ground State Energies ◽  
Second Order Perturbation Theory

Applications of the multireference linearized coupled-cluster single-doubles (MRLCCSD) to atomic and molecular systems have been carried out. MRLCCSD is exploited to calculate the ground-state energies of HF, H2O, NH3, CH4, N2, BF, and C2with basis sets, cc-pVDZ, cc-pVTZ and cc-pVQZ. The equilibrium bond lengths and vibration frequencies of HF, HCl, Li2, LiH, LiF, LiBr, BH, and AlF are computed with MRLCCSD and compared with the experimental data. The electron affinities of F and CH as well as the proton affinities of H2O and NH3are also calculated with MRLCCSD. These results are compared with the results produced with second-order perturbation theory, linearized coupled-cluster doubles (LCCD), coupled-cluster doubles (CCD), coupled-cluster singles and doubles (CCSD), CCSD with perturbative triples correction (CCSD(T)). It is shown that all results obtained with MRLCCSD are reliable and accurate.

scholarly journals Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions

2016 ◽  
Vol 144 (19) ◽  
pp. 194103 ◽  
Author(s):  
Janus J. Eriksen ◽  
Devin A. Matthews ◽  
Poul Jørgensen ◽  
Jürgen Gauss
Keyword(s):  
Perturbation Theory ◽  
Open Shell ◽  
Coupled Cluster ◽  
Cluster Perturbation Theory

scholarly journals Ground State Energies of Helium-Like Ions Using a Simple Parameter-Free Matrix Method

2021 ◽  
Vol 21 (4) ◽  
pp. 1003
Author(s):  
Redi Kristian Pingak ◽  
Atika Ahab ◽  
Utama Alan Deta
Keyword(s):  
Wave Function ◽  
Perturbation Theory ◽  
Ground State ◽  
Matrix Method ◽  
Variational Approach ◽  
Geometrical Model ◽  
Variational Parameter ◽  
Analytic Expression ◽  
Ground State Energies ◽  
Simple Parameter

This study aims to use hydrogenic orbitals within an analytic and numeric parameter-free truncated-matrix method to solve the projected Schrödinger equation of some Helium-like ions (3 ≤ Z ≤ 10). We also derived a new analytical expression of the ion ground state energies, which was simple and accurate and improved the accuracy of the analytic calculation, numerically using Mathematica. The standard matrix method was applied, where the wave function of the ions was expanded in a finite number of eigenvectors comprising hydrogenic orbitals. The Hamiltonian of the systems was calculated using the wave function and diagonalized to obtain their ground state energies. The results showed that a simple analytic expression of the ground state energies of He-like ions was successfully derived. Although the analytic expression was derived without involving any variational parameter, it was reasonably accurate with a 0.12% error for Ne8+ ion. From this method, the accuracy of the analytic energies was also numerically improved to 0.10% error for Ne8+ ion. The results clearly showed that the energies obtained using this method were more accurate than the hydrogenic perturbation theory and the uncertainty principle-variational approach. In addition, for Z > 4, our results were more accurate than those from the geometrical model.

scholarly journals Equation-of-motion coupled cluster perturbation theory revisited

2014 ◽  
Vol 140 (17) ◽  
pp. 174114 ◽  
Author(s):  
Janus J. Eriksen ◽  
Poul Jørgensen ◽  
Jeppe Olsen ◽  
Jürgen Gauss
Keyword(s):  
Perturbation Theory ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Cluster Perturbation Theory
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