Vacuum Fluctuations and Intermolecular Interactions

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Abstract
The electromagnetic field operators in the vicinity of a neutral molecule are obtained in the Heisenberg picture. The fields are found using the multipolar Hamiltonian and the interaction includes electric dipole, magnetic dipole, electric quadrupole, and diamagnetic couplings. These fields are used to calculate the dispersion energy between two neutral molecules. The dispersion energy may be obtained by treating one molecule as a test body and calculating its response to the field of the other. A note-worthy feature of this test-body approach is that the energy expressions so obtained are valid for all intermolecular separations outside overlap and retardation effects are fully taken into account. The method is applied to the calculation of dispersion energy between a pair of molecules with different polarizability characteristics. The contribution of the diamagnetic coupling to the energy shift is also presented. The theory is adapted to the calculation of N-molecule dispersion interactions and applied to 3- and 4-molecule systems.