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Applicability of MNDO techniques AM1 and PM3 to ring-structured polymers
1Instituto de Física, USP, CP 66318, São Paulo, SP, Brazil.
Journal of Computational Chemistry
|July 13, 2002
Summary
Semiempirical methods like AM1 accurately predict ground state geometries for ring-structured molecules, making them suitable for studying complex conducting polymers. This research validates their use in computational chemistry for conjugated systems.
Area of Science:
- Computational Chemistry
- Materials Science
- Quantum Chemistry
Background:
- Semiempirical Hartree-Fock techniques are commonly used for ring-structured chains.
- These methods were not originally parameterized for such systems, necessitating validation.
Purpose of the Study:
- To assess the applicability of NDDO family methods (MNDO, AM1, PM3) for ground state geometries of ring-structured molecules.
- To compare these results with high-level ab initio calculations.
Main Methods:
- Calculated ground state geometries of orthobenzoquinone, its dimers, and polyaniline trimers.
- Employed semiempirical methods: MNDO, AM1, and PM3.
- Validated against ab initio Restricted Hartree-Fock 6-31G(d,p) and Møller-Plesset 2 perturbation theory.
Main Results:
- AM1 demonstrated qualitative agreement with ab initio results across all investigated systems.
- MNDO and PM3 showed less consistent agreement compared to AM1.
- The torsion angle between rings, crucial for electronic properties, was a key focus.
Conclusions:
- AM1 is recommended for studying the geometries and properties of longer, complex conjugated polymers with ring structures.
- Semiempirical methods, particularly AM1, offer a computationally efficient alternative for relevant chemical systems.