Ground state structures and excited state dynamics of pyrrole-water complexes: Ab initio excited state molecular dynamics simulations

Abstract

Structures of the ground state pyrrole-(H2O)(n) clusters are investigated using ab initio calculations. The charge-transfer driven femtosecond scale dynamics are studied with excited state ab initio molecular dynamics simulations employing the complete-active-space self-consistent-field method for pyrrole-(H2O)(n) clusters. Upon the excitation of these clusters, the charge density is located over the farthest water molecule which is repelled by the depleted pi-electron cloud of pyrrole ring, resulting in a highly polarized complex. For pyrrole-(H2O), the charge transfer is maximized (up to 0.34 a.u.) around similar to 100 fs and then oscillates. For pyrrole-(H2O)(2), the initial charge transfer occurs through the space between the pyrrole and the pi H-bonded water molecule and then the charge transfer takes place from this water molecule to the sigma H-bonded water molecule. The total charge transfer from the pyrrole to the water molecules is maximized (up to 0.53 a.u.) around similar to 100 fs. (c) 2008 American Institute of Physics.