Chemisorption theory

The aim of chemisorption theory is to achieve for any adsorbateladsorbent system complete quantum predictions of the equilibrium positions of all the nuclei, the ground-state (electronically adiabatic) potential energy surface, the electronic excitation spectrum, and the response of the system to external probes. We are still a very long way from this goal, but some simplified models can now be explored in depth. Serious quantitative work begins with Toya,^1,2 and my review ends with the work of Appelbaum and Hamann³ These works provide examples of two of the three approaches to chemisorption theory. Toya's is a configuration interaction (CI) approach, using the states of the noninteracting adsorbate/solid system as basis states; Appelbaum and Hamann try to integrate Schrodinger's equation directly. The third approach is the linear combination of atomic orbitals molecular orbital (LCAO-MO) theory, and I begin with it because it is generally familiar in its simpler forms through its widespread use in molecular quantum mechanics. However, I remark at this stage that the direct integration of Schrodinger's equation may be more economical in computer time than the traditional quantum chemistry approach; it is certainly more economical if the nonlocal Hartree-Fock exchange potential is replaced by a local approximation to it.