We have proposed the model space quantum Monte Carlo (MSQMC) method, which stochastically samples the contribution from a large secondary space to the effective Hamiltonian in the energy dependent partitioning of L�wdin [1]. The method treats quasi-degenerate electronic states on a target energy with bond dissociations and electronic excitations avoiding significant amount of the negative sign problem. We demonstrage the performance of the method on the ground and excited states of model systems including H4 and N2 at various configurations. We also discuss F12 extensions of the method for accelerating the basis set convergence in connection to the projector QMC method in the configuration space in conjunction with an F12 similarity-transformed Hamiltonian [2]. The method virtually attains the full CI and complete basis set (CBS) limits at modest computational costs.[1] S. Ten-no, arXiv:1302.3924 (2013).[2] Y. Ohtsuka and S. Ten-no, AIP Conference Proceedings, 1456 , 97 (2012).

Model space quantum Monte Carlo method for full CI solutions of quasi-degenerate electronic states

246th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.