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Subvalence Orbitals and Diffuse Functions in Accurate Electronic Structure Calculations: Insights from Nitrogenase
Dayou Zhang1, Maryam Mansoori Kermani1, Donald G Truhlar1
1Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States.
The Journal of Physical Chemistry Letters
|August 8, 2025
Summary
Including additional subvalence basis functions significantly impacts electronic structure calculations for metal-ligand complexes, improving accuracy in unrestricted second-order Møller-Plesset perturbation theory (UMP2) energy differences.
Area of Science:
- Computational chemistry
- Quantum chemistry
- Electronic structure theory
Background:
- Metal-ligand complexes are crucial in biological systems, such as nitrogenase enzymes.
- Accurate electronic structure calculations are essential for understanding their properties.
- Previous studies have used simplified models of iron-sulfur clusters.
Purpose of the Study:
- To investigate the impact of diffuse functions and additional subvalence basis functions on electronic structure calculations.
- To evaluate these effects on unrestricted Hartree-Fock (UHF) and unrestricted second-order Møller-Plesset perturbation theory (UMP2) calculations.
- To determine the influence on relative energies of Fe-S dimer clusters, models for nitrogenase.
Main Methods:
- Performed unrestricted Hartree-Fock (UHF) and unrestricted second-order Møller-Plesset perturbation theory (UMP2) calculations.
- Utilized varying basis sets on four Fe-S dimer clusters.
- Analyzed the influence of diffuse functions and additional subvalence basis functions on calculated energies.
Main Results:
- Diffuse functions and additional subvalence basis functions had minimal impact on UHF relative energies.
- Diffuse functions showed minimal effects on UMP2 relative energies.
- Additional subvalence basis functions significantly affected UMP2 relative energies, causing underestimations by up to 2.7 kcal/mol when neglected.
Conclusions:
- Additional subvalence basis functions are critical for accurate UMP2 calculations of these Fe-S dimer clusters.
- Neglecting these functions leads to significant underestimation of energy differences.
- A revised composite method incorporating these basis functions is proposed for improved benchmark values.
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