The overall objectives of this project are to discover, test and apply the correct theoretical principles governing molecular electronic structure, with the specific focus the problem of understanding changes of molecular conformation, especially molecular vibrations far from equilibrium. Employed are calculations solving the Schrodinger equation, formal analysis based on the equation, and experimental spectroscopic data. Development of basic concepts is emphasized, with special attention to the role of electron density and energy-density functionals. BIBLIOGRAPHIC REFERENCES: Long-range behavior of natural orbitals and electron density. M. Levy and R.G. Parr, J. Chem. Phys., 64, 2707-2708 (1976). Direct determination of the rotational barrier in ethane using perturbation theory, Tsun-Shi Nee, R.G. Parr and Rodney J. Bartlett, J. Chem. Phys., 64, 2216-2225 (1976).