All-quantum description of molecules: electrons and nuclei of C6H6

Feynman path integral (FPI) quantum Monte Carlo simulations have been combined with electronic ab initio calculations of Hartree-Fock (HF) type to achieve an all-quantum description of the benzene molecule. The linking of these two quantum approaches allows the consideration of the quantum character of the atomic nuclei and electrons. The FPI formalism has been employed to generate 6000 different nuclear configurations of the benzene molecule which are populated in thermal equilibrium (canonical ensemble statistics). In a second step the ab initio HF Hamiltonian has been used to calculate (electronic) expectation values as ensemble averages over these configurations. The influence of the nuclear dynamics on the kinetic and potential energy of the electronic Hamiltonian is discussed. The spatial nuclear degrees of freedom of benzene are largely determined by quantum fluctuations which exceed the thermal fluctuations even at room temperature. The importance of the quantum delocalization of the nuclei is emphasized on the basis of calculated radial and angular distribution functions.