Quantum dynamics via adiabatic ab initio centroid molecular dynamics

The ab initio path integral simulation method is combined with centroid molecular dynamics. This unification, and thus extension of these basic techniques, allows for the investigation of the real-time quantum dynamics in chemically complex many-body systems. The theory underlying the proposed ab initio centroid molecular dynamics (AICMD) technique is presented in detail. The real-time propagation of the nuclei is obtained in the quasiclassical approximation within the framework of centroid path integrals. Concurrently, the forces acting on the nuclei are computed from 'on the fly' electronic structure calculations based on first-principle techniques such as, e.g., Hohenberg-Kohn-Sham density functional theory. AICMD can be considered as a quasiclassical generalization of standard Car-Parrinello ab initio molecular dynamics. At the same time, AICMD preserves the virtues of the ab initio path integral technique to generate exact time-independent quantum equilibrium averages. AICMD is well suited to investigate, in a quasiclassical sense, the real-time evolution of molecular quantum systems with complex interactions which cannot be satisfactorily represented by simple model potentials. In particular, the method permits the simulation of the dynamics of chemical reactions including quantum effects. AICMD is applicable to isolated systems in the gas phase such as molecules, clusters or complexes as well as to condensed matter, i.e. molecular liquid or solids.