Daniel Adu-Gyamfi

• University of Cape Coast

The author demonstrates in a simple way, using a unitary transformation, the general gauge invariance of linear response theory.

We propose a novel way of identifying the electric and magnetic response of a system in an external electromagnetic field, illustrating in particular with the current density response.

We calculate the orientational average of the total electric dipole and quadrupole moments of a polar molecule in a non-uniform electric field and comment on the results.

We study the electric quadrupole density of an isotropic non-polar fluid as a response to the microscopic gradient of the electric fields at the centres of the molecules in the fluid. This contribution to the macroscopic quadrupole tensor is shown to have zero trace. Furthermore we discuss the problem of dispersion in media with only induced electr...

The theory of propagation of light through a medium of molecules with induced multipole moments of arbitrary order is studied. Positional and orientational correlations between molecules are neglected. A central result is the generalization of Lorentz's expression for the average local field acting on a molecule to a medium with higher multipole de...

The nonrelativistic hamiltonian for a molecule in the presence of non-uniform, time-dependent electric and magnetic fields is transformed to multipole form by means of a canonical transformation.