Almost exact energies for the Gaussian-2 set with the semistochastic heat-bath configuration interaction method

Yuan Yao (1) , Emmanuel Giner (2) , Junhao Li (1) , Julien Toulouse (2, 3) , C. J Umrigar (1)

1 LASSP - Laboratory of Atomic and Solid State Physics [Ithaca]
2 LCT - Laboratoire de chimie théorique
3 IUF - Institut universitaire de France

The recently developed semistochastic heat-bath configuration interaction (SHCI) method is a systematically improvable selected configuration interaction plus perturbation theory method capable of giving essentially exact energies for larger systems than is possible with other such methods. We compute SHCI atomization energies for 55 molecules which have been used as a test set in prior studies because their atomization energies are known from experiment. Basis sets from cc-pVDZ to cc-pV5Z are used, totaling up to 500 orbitals and a Hilbert space of 10 32 Slater determinants for the largest molecules. For each basis, an extrapolated energy well within chemical accuracy (1 kcal/mol or 1.6 mHa/mol) of the exact energy for that basis is computed using only a tiny fraction of the entire Hilbert space. We also use our almost exact energies to benchmark coupled-cluster [CCSD(T)] energies. The energies are extrapolated to the complete basis set limit and compared to the experimental atomization energies. The extrapolations are done both without and with a basis-set correction based on density-functional theory. The mean absolute deviations from experiment for these extrapolations are 0.46 kcal/mol and 0.51 kcal/mol, respectively. Orbital optimization methods used to obtain improved convergence of the SHCI energies are also discussed.

Domaines: Chimie théorique et/ou physique; Chimie-Physique [physics.chem-ph]

Yuan Yao, Emmanuel Giner, Junhao Li, Julien Toulouse, C. J Umrigar. Almost exact energies for the Gaussian-2 set with the semistochastic heat-bath configuration interaction method. Journal of Chemical Physics, 2020, 153 (12), pp.124117. ⟨10.1063/5.0018577⟩. ⟨hal-02991165⟩