Electrostatic interactions moving point charge

Molecules do not consist of rigid arrays of point charges, and on application of an external electrostatic field the electrons and protons will rearrange themselves until the interaction energy is a minimum. In classical electrostatics, where we deal with macroscopic samples, the phenomenon is referred to as the induced polarization. I dealt with this in Chapter 15, when we discussed the Onsager model of solvation. The nuclei and the electrons will tend to move in opposite directions when a field is applied, and so the electric dipole moment will change. Again, in classical electrostatics we study the induced dipole moment per unit volume. 

As we have mentioned before, the complete non-relativistic Hamiltonian for a system of point charges interacting electrostatically and moving through field-free space can be written in the form... 

When an electric field E is applied to the cell, there is an interaction between E and P, which forces the director to move around the cone to a point of equilibrium. If the field is changed, the director moves again. The phase adopts a structure in which the n director precesses helically around the cone from layer to layer to minimize the electrostatic interaction with the side dipoles, thus destroying any bulk spontaneous charge separation. 

In the Drude oscillator model, the polarization effect is described by a point charge (the Drude oscillator) attached to each nonhydrogen atom via a harmonic spring. The point charge can move relative to the attachment site in response to the electrostatic environment. The electrostatic energy is the sum of the pairwise interactions between atomic charges and the partial charge of the Drude particles... 

All science is based on a number of axioms (postulates). Quantum mechanics is based on a system of axioms that have been formulated to be as simple as possible and yet reproduce experimental results. Axioms are not supposed to be proved, their justification is efficiency. Quantum mechanics, the foundations of which date from 1925-26, still represents the basic theory of phenomena within atoms and molecules. This is the domain of chemistry, biochemistry, and atomic and nuclear physics. Further progress (quantum electrodynamics, quantum field theory, elementary particle theory) permitted deeper insights into the structure of the atomic nucleus, but did not produce any fundamental revision of our understanding of atoms and molecules. Matter as described at a non-relativistic quantum mechanics represents a system of electrons and nuclei, treated as point-like particles with a definite mass and electric charge, moving in three-dimensional space and interacting by electrostatic forces. This model of matter is at the core of quantum chemistry. Fig. 1.2. 

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