Long-range forces between polar alkali-metal diatoms aligned by external electric fields

Long-range electrostatic, induction, and dispersion coefficients including terms of order R ^-8 have been calculated by the sum over states method using time-dependent density-functional theory. We also computed electrostatic moments and static polarizabilities of the individual diatoms up to the octopole order using coupled-cluster and density-functional theory. The laboratory-frame transformed electrostatic moments and van der Waals coefficients corresponding to the alignment of the diatomic molecules were found. We use this transformation to obtain the coupling induced by an external dc electric field and present values for all XY combinations of like polar alkali-metal diatomic molecules with atoms from Li to Cs. Analytic solutions to the dressed-state laboratory-frame electrostatic moments and long-range intermolecular potentials are also given for the dc low-field limit.