A multireference coupled-electron pair approximation combined with complete-active space perturbation theory in local pair-natural orbital framework

2020 ◽  
Vol 152 (11) ◽  
pp. 114111
Author(s):  
Masaaki Saitow ◽  
Takeshi Yanai
Keyword(s):  
Perturbation Theory ◽  
Electron Pair ◽  
Pair Approximation ◽  
Natural Orbital ◽  
Complete Active Space ◽  
Active Space ◽  
Local Pair

Implementation of the interacting quantum atoms energy decomposition with the CASPT2 method

2021 ◽  
Author(s):  
Jesús Jara-Cortés ◽  
Edith Leal-Sánchez ◽  
Evelio Francisco ◽  
Jose A. Perez-Pimienta ◽  
Ángel Martín Pendás ◽  
...  
Keyword(s):  
Perturbation Theory ◽  
Real Space ◽  
Order Perturbation ◽  
Order Perturbation Theory ◽  
Energy Decomposition ◽  
Complete Active Space ◽  
Active Space ◽  
Decomposition Scheme ◽  
Interacting Quantum Atoms ◽  
Second Order Perturbation Theory

We present an implementation of the interacting quantum atoms energy decomposition scheme (IQA) with the complete active space second-order perturbation theory (CASPT2). This combination yields a real-space interpretation tool with...

scholarly journals The RASSCF, RASSI, and CASPT2 Methods Used on Small Molecules of Astrophysical Interest

1994 ◽  
Vol 146 ◽  
pp. 338-352
Author(s):  
Per-Åke Malmqvist
Keyword(s):  
Perturbation Theory ◽  
Small Molecules ◽  
Stellar Atmosphere ◽  
Second Order ◽  
Cloud Chemistry ◽  
Complete Active Space ◽  
Active Space ◽  
Computational Quantum Chemistry ◽  
Self Consistent Field ◽  
Far From Equilibrium

To a quantum chemist with no particular background in astrophysics or astronomy, a brief glance at journals and textbooks in these fields shows at least three areas where computational quantum chemistry has had a valuable impact: Interstellar cloud chemistry; stellar atmosphere modelling; and chemistry in extreme conditions, such as at the surface of a neutron star. The first two uses are particularly suitable, since standard methods are directly applicable.For such problems, good calculations of potential energy as well as expectation values and matrix elements of dipole and other operators appears to be in demand. Many electronic states may be involved, at least a broad range of problems involve fairly small molecules, often radicals, and conformation regions far from equilibrium. Such problems are addressed by three methods originated in our laboratory, and known by the acronyms RASSCF (Restricted Active Space Self-Consistent Field, Malmqvist et al. 1990), RASSI (RAS State Interaction) and CASPT2 (Complete Active Space Perturbation Theory to Second Order-Complete Active Space Perturbation Theory to Second Order, Andersson et al. 1990; Andersson et al. 1992).

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