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Second-Order Complete Active Space Perturbation Theory (CASPT2) and N-Electron Valence State Perturbation Theory
1Department of Chemistry, Chungbuk National University (CBNU), Cheongju 28644, Korea.
Abstract:
We have developed the second-order complete active space perturbation theory (CASPT2) and N-electron valence state perturbation theory (NEVPT2) based on the adaptive sampling configuration interaction self-consistent field (ASCI-SCF) reference function. Our method directly calculates the intermediate matrices needed for the CASPT2 and NEVPT2 calculations to reduce the memory required for storing the four-particle reduced density matrix (4RDM). To demonstrate the method's applicability, we evaluated the singlet-triplet gaps in several polyacenes and the potential energy curves of chromium dimer, in which the largest active space we tested was (34e,34o).
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