Abstract: Based on the three methods of Mulliken, Stoutpolitzer and SCPA, we calculated the contribution of basis function of the frontier molecular orbital components of alanine (Ala) chiral enantiomers, respectively. The results show that three methods are used to calculate the contribution of basis function of the 20th molecular orbital component, the 5th and 9th basis functions, the qualitative conclusion that describes the maximum contribution of the basis functions describing the 2pz atom orbits of 1N atom is consistent. The 2p atomic orbital shells of each atom have limited contribution to the molecular orbits near the nucleus. The contribution to the 15—20 occupying orbit is more complicated, the results of 2p atomic orbital shell contribution of 1N,3C,5C atoms are consistent, the contribution of the 2p atomic orbital shell of 6C and 10O atoms is quite different.

Key words: alanine, orbital component, atomic orbital shell, basis function