Construction of electronic diabatic states within a molecular orbital scheme

A new procedure is proposed to construct a diabatic representation that is readily implemented in the molecular orbital-self-consistent field-configuration interaction scheme. It is based on the calculation of adiabatic wave functions at a reference geometry Q(0) and of the appropriate modifications to be made to molecular orbitals for Qnot equalQ(0) in order to force the derivative couplings for all electronic states to be exactly zero in the space around Q(0). This approach is applied to the construction of the diabatic basis and to the calculation of the associated (adiabatic) vibronic coupling for a number of well-characterized systems. The properties and the limitations of this diabatic basis are discussed. (C) 2003 American Institute of Physics.