Polarized Molecular Orbital Model Chemistry. I. Ab Initio Foundations

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate simulation of electronic polarization effects is essential in computational chemistry.
• Current semiempirical molecular orbital methods have limitations in simulating polarization.
• Developing improved methods requires understanding minimal basis set requirements.

Purpose of the Study:

• To determine the minimal requirements for semiquantitative molecular polarizabilities.
• To establish a foundation for a new semiempirical molecular orbital formulation.
• To enhance the simulation of electronic polarization effects.

Main Methods:

• Performed polarizability calculations for 38 molecules.
• Utilized 36 distinct basis sets, including unconventional ones.
• Employed five semiempirical molecular orbital theories based on neglect of diatomic differential overlap (NDDO).

Main Results:

• Identified two promising basis sets for semiempirical improvement: STO-3G(,P) and 3-(21,3,21)G.
• STO-3G(,P) adds diffuse p functions to hydrogen atoms.
• 3-(21,3,21)G augments a minimal basis set with an extra s function on each atom.

Conclusions:

• STO-3G(,P) is particularly recommended due to zero intra-atomic overlap integrals by symmetry.
• This property makes STO-3G(,P) suitable for NDDO treatments.
• The findings provide a basis for developing more accurate semiempirical methods for polarization effects.