Open AccessMultistate Complete-Active-Space Second-Order Perturbation Theory Based on Density Matrix Renormalization Group Reference States
Author(s) -
Takeshi Yanai,
Masaaki Saitow,
Xiao-Gen Xiong,
Jakub Chalupský,
Yuki Kurashige,
S.Y. Guo,
Sandeep Sharma
Publication year - 2017
Publication title -
journal of chemical theory and computation
Language(s) - Uncategorized
Resource type - Journals
SCImago Journal Rank - 2.001
H-Index - 185
eISSN - 1549-9626
pISSN - 1549-9618
DOI - 10.1021/acs.jctc.7b00735
Subject(s) - density matrix renormalization group , complete active space , hamiltonian (control theory) , rdm , wave function , physics , renormalization group , quantum mechanics , computer science , mathematics , density functional theory , basis set , mathematical optimization , computer network
We present the development of the multistate multireference second-order perturbation theory (CASPT2) with multiroot references, which are described using the density matrix renormalization group (DMRG) method to handle a large active space. The multistate first-order wave functions are expanded into the internally contracted (IC) basis of the single-state single-reference (SS-SR) scheme, which is shown to be the most feasible variant to use DMRG references. The feasibility of the SS-SR scheme comes from two factors: first, it formally does not require the fourth-order transition reduced density matrix (TRDM) and second, the computational complexity scales linearly with the number of the reference states. The extended multistate (XMS) treatment is further incorporated, giving suited treatment of the zeroth-order Hamiltonian despite the fact that the SS-SR based IC basis is not invariant with respect to the XMS rotation. In addition, the state-specific fourth-order reduced density matrix (RDM) is eliminated in an approximate fashion using the cumulant reconstruction formula, as also done in the previous state-specific DMRG-cu(4)-CASPT2 approach. The resultant method, referred to as DMRG-cu(4)-XMS-CASPT2, uses the RDMs and TRDMs of up to third-order provided by the DMRG calculation. The multistate potential energy curves of the photoisomerization of diarylethene derivatives with CAS(26e,24o) are presented to illustrate the applicability of our theoretical approach.