Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Theory, Implementation, and Parameters.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Standard semiempirical methods like MNDO have limitations in accurately predicting molecular properties.
• Incorporating additional interactions such as Pauli repulsion and penetration effects can enhance theoretical models.

Purpose of the Study:

• To detail the theoretical formalism and implementation of OM1, OM2, and OM3 methods.
• To provide parameters for OMx methods for key elements (H, C, N, O, F).
• To evaluate the performance of OMx methods for molecular properties.

Main Methods:

• Development and implementation of orthogonalization-corrected semiempirical methods (OM1, OM2, OM3).
• Inclusion of Pauli repulsion, penetration effects, and core-valence interactions in the Fock matrix.
• Parametrization of OMx methods for H, C, N, O, and F.
• Addition of Grimme-type dispersion corrections to OM2 and OM3.

Main Results:

• OMx methods demonstrate systematic improvements for ground- and excited-state properties compared to standard MNDO.
• OMx methods show superior performance for a set of organic molecules.
• Dispersion-corrected OM2 and OM3 accurately model noncovalent interactions in molecular complexes (S22, S66×8).

Conclusions:

• OMx methods represent a significant advancement over traditional semiempirical approaches.
• The OMx methods provide a robust and accurate framework for computational chemistry.
• The inclusion of dispersion corrections further enhances the applicability of OMx for studying intermolecular forces.