Accelerated One-Step Density Matrix Renormalization Group Self-Consistent Field Method

Abstract

CASSCF (Complete Active Space Self-Consistent Field) computes the exact FCI (Full-Configuration Interaction) wavefunction for valence electrons within a user-designated active space, and becomes a standard multi-reference method for computing non-dynamic electronic correlations of strongly correlated molecule. DMRG (Density Matrix Renormalization Group)-based CASSCF (DMRGSCF) allows to treat a large active space which is beyond the limit of conventional CASSCF. However, all reported DMRGSCF methods in literature are based on the two-step optimization in which molecular orbitals (MOs) and CI wavefunction parameters are optimized separately. Apparently the caveat in any two-step procedure is that when orbitals and wavefunction are strongly coupled, or an active space is not wisely chosen, it leads to a rather slow iterative convergence and sometimes even a serious divergence problem. In this talk, I will present our recent progress in developing a one-step DMRGSCF procedure in which the second-order optimization is carried out for both MOs and wavefunctions simultaneously. Our algorithm, implementation and numerical results will be discussed to demonstrate an accelerated convergence of otherwise challenging examples.