Ab initio path integral Monte Carlo simulations for water trimer with electron correlation effects

We have performed ab initio path integral Monte Carlo simulations for water trimer (H2O)3 system. The electron correlation effects have been taken into account up to the level of third-order Møller-Plesset (MP3) perturbation theory. Through comparisons of calculated geometrical properties of water trimer such as O–O distance, O–H–O angle, and torsional angle between O–H and O–O–O plane, the interplays among the nuclear quantum, thermal and electron correlation effects are analyzed quantitatively.