| The scientific field that serves to establish connections between the experimental results from studies of atomic and molecular systems through the physical theories of minimization principles, Maxwell's equations, and statistical mechanics.
The physical theories listed here are not strictly inclusive, as various phenomenological results are applied to specific systems in order to solve specific problems. Nevertheless, all of mechanics including quantum mechanics may in principle be derived from the minimization of an expression for the lagrangian or hamiltonian density of a system. In this sense, even statistical mechanics is not truly independent as a physical theory.
For a completely rigorous treatment of atomic and molecular systems, the results of both special and general relativity must also be taken into account. But it can often be shown that the terms in the equations of motion that result from relativity are not significant for atomic and molecular systems. | 
