Orbital Analysis

Abstract

In Hartree-Fock equation, the obtained wave-function represents atomic orbitals in atom and molecular orbitals in molecule. The details of chemical bonding and charge density can be investigated from orbital analysis. Chemical bonding rule is very useful to specify chemical bonding character. Outer shell electron is shared between different atoms in covalent bonding, though different atoms are bound through Coulomb interaction in ionic bonding. Hence, chemical bonding character can be specified by checking whether orbital overlap exists or not in molecular orbital including outer shell electrons. Mulliken charge density is a useful index to estimate a net electron distribution. As orbital overlap is equally divided into different atoms, it may cause an error. However, it has been widely accepted that Mulliken charge density is applicable for a quantitative discussion. In wave-function, spin-orbital interaction is taken into account, through the product between spatial orbital and spin function. The communication relation exists between Hamiltonian and spin operator. Natural orbital is completely different from molecular orbital. The discrete orbital energy disappears, and α and β spin functions are mixed.