Abinitioinstanton molecular dynamics for the description of tunneling phenomena

A general method is presented for ab initio dynamical simulation of tunneling processes in solids and molecules, including both nuclear and spin degrees of freedom. This technique accounts for the adiabatic evolution of the potential associated with the nuclear and spin degrees of freedom in tunneling processes, in contradistinction to semiempirical approaches. To illustrate the method, inversion splitting in ${\mathrm{NH}}_3$, ${\mathrm{ND}}_3$, and ${\mathrm{PH}}_3$ is calculated within the local-density approximation. © 1996 The American Physical Society.