Competitive nuclear quantum effect and H/D isotope effect on torsional motion of H2O2: An ab initio path integral molecular dynamics study

Ab initio path integral molecular dynamics (PIMD) simulations were performed to understand the nuclear quantum effect and thermal effect on the torsional motion of H2O2 (D2O2). A broad distribution of geometrical parameters (OH and OO bond lengths [ROH and ROO] and HOO bond angle [∠HOO]) was obtained in quantum ab initio PIMD simulations, rather than in classical MD simulations. However, a modest distribution around the trans-configuration TS (∠HOOH = 180°) was found in the quantum ab initio PIMD simulations of H2O2 at low temperatures. Thus, the nuclear quantum effect slightly enhanced the HOOH torsional motion at low temperatures. A series of simulations also revealed that the thermal effect enhanced the HOOH torsional motion. However, it was restrained by the primary nuclear quantum effect on the ROH in quantum simulations at high temperatures. Therefore, an interesting competitive nuclear quantum effect on the torsional motion of H2O2 was observed.