"Selected CI and Jastrow-free QMC methods for Chemistry"

Who: Pierre-Francois Loos, CNRS Universite Paul Sabatier (Toulouse)

Place: Donostia International Physics Center

Date: Monday, 17 December 2018, 12:00

In this talk, I will present some of our recent advances on selected configuration interaction (sCI) and quantum Monte Carlo (QMC) methods [1, 2, 3, 4, 5]. In particular, I will detail our protocol to deterministically construct nodal surfaces within QMC using the sCI algorithm CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) [2, 4, 5]. In contrast to standard QMC implementations, these nodes can be systematically and deterministically improved by increasing the size of the sCI expansion. The present methodology will be illustrated on the transition metal sulfide molecule FeS [2], which is particularly challenging due to the proximity of two low-energy electronic states of different spatial symmetry. Results on the excited states of small organic molecules will also be presented, and we are going to show that, by using small multideterminant expansions without Jastrow factor, one can obtain highly accurate vertical transition energies [4].

[1] Hybrid stochastic-deterministic calculation of the second-order perturbative contribution of mul- tireference perturbation theory, Y. Garniron, A. Scemama, P. F. Loos and M. Caffarel. J. Chem. Phys. 147, 034101 (2017).
[2] Deterministic construction of nodal surfaces within quantum Monte Carlo: the case of FeS, A. Scemama, Y. Garniron, M. Caffarel and P. F. Loos, J. Chem. Theory Comput.
14, 1395 (2018).
[3] A mountaineering strategy to excited states: highly-accurate reference energies and
benchmarks, P. F. Loos, A. Scemama, A. Blondel, Y. Garniron, M. Caffarel and D.
Jacquemin, J. Chem. Theory Comput. (submitted).
[4] Excitation energies from diffusion Monte Carlo using selected configuration
interaction nodes, A. Scemama, A. Benali, D. Jacquemin, M. Caffarel and P. F. Loos, J.
Chem. Phys. 149, 034108 (2018).
[5] Selected configuration interaction dressed by perturbation, Y. Garniron, A.
Scemama, E. Giner, M. Caffarel and P. F. Loos, J. Chem. Phys. 149, 064103 (2018).

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