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) t ype to achieve an all-quantum description of the benzene molecule. The linking of these two quantum approaches allows the consideration of t he quantum character of the atomic nuclei and electrons. The FPI forma lism has been employed to generate 6000 different nuclear configuratio ns of the benzene molecule which are populated in thermal equilibrium (canonical ensemble statistics). In a second step the ab initio HF Ham iltonian has been used to calculate (electronic) expectation values as ensemble averages over these configurations. The influence of the nuc lear dynamics on the kinetic and potential energy of the electronic Ha miltonian is discussed. The spatial nuclear degrees of freedom of benz ene are largely determined by quantum fluctuations which exceed the th ermal fluctuations even at room temperature. The importance of the qua ntum delocalization of the nuclei is emphasized on the basis of calcul ated radial and angular distribution functions. (C) 1997 Elsevier Scie nce B.V.