Scaled diatomics-in-molecules (SDIM) theory. I. General theory and preliminary applications to H3 and H4

Abstract

Diatomics‐in‐molecules (DIM) is an established semiempirical theory for calculating atomization energies and potential energy surfaces for polyatomic systems in ground and excited states. A fundamental deficiency of this method must be considered its omission of optimum scaling of the diatomic and polyatomic wave functions. A new scaled DIM (SDIM) theory is proposed which utilizes a basis of scaled exact atomic state eigenfunctions. Scaled atoms‐in‐molecules (SAIM) theory [Theor. Chim. Acta 51, 241 (1979)] is employed to generate approximate optimumly scaled diatomic fragment eigenfunctions. Rigorous theory is formulated for independent variational scaling of polyatomic state functions using established DIM algorithms. Polyatomic eigenvalue equations are solved in terms of diatomic and monatomic eigenvector and empirical eigenvalue input; no complex electronic integral computations are required, except for overlap (as in ordinary DIM theory) and kinetic energy integrals. Initial applications to H₃ and H₄ using a minimal basis set are reported.