Quantum Monte Carlo study of small hydrocarbon atomization energies

Abstract

A benchmark study of atomization energies is reported for 22 hydrocarbons using single determinant trial functions in the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo (QMC) method. The DMC atomization energies are compared to experiment, a complete basis set approach (CBS-Q), density functional theory with the B3LYP functional, and coupled-cluster singles, doubles and perturbative triples, CCSD(T), methods. Comparison of the DMC results to experiment yields a mean absolute deviation of 1.9kcalmol−1, which is comparable to that of the B3LYP/cc-pVQZ (1.7kcalmol−1) level of theory, but less accurate than that of CBS-Q (1.1kcalmol−1). DMC performs similarly for both closed-shell and open-shell molecules with mean absolute deviations of 2.1kcalmol−1 for the former and 1.7kcalmol−1 for the latter systems. The use of experimental zero-point energies (ZPEs), rather than scaled B3LYP ZPEs, is found to have negligible effect on DMC atomization energies. The latter reported here provide a baseline from which further improvement in the calculation of DMC atomization energies, including the use of multi-determinant and other trial function improvements, can be measured.