Calculation of dipole moment functions with density functional theory: application to vibrational band intensities

We have calculated fundamental and overtone XH stretching vibrational band intensities for H2O, benzene, cyclohexane, 1,3-butadiene, and HCN. The band intensities were calculated with a simple harmonically coupled anharmonic oscillator local mode model and a series expanded dipole moment function. T he dipole moment functions were obtained from local, non-local and hybrid d ensity functional theory calculations with basis sets ranging from 6-31G(d) to 6-311++G(3df,3pd). The calculated band intensities have been compared w ith intensities calculated with conventional ab initio methods and with exp erimental results. Compared with conventional correlated ab initio methods, a carefully chosen density functional method and basis set seems to give b etter fundamental and overtone intensities with far less resources used. We have found that the density functional methods appear to be less sensitive to the choice of basis set, with little difference between the results obt ained with a non-local or hybrid density functional method.