The Grassmann interpolation method for spin-unrestricted open-shell systems.

Area of Science:

• Computational Chemistry
• Quantum Chemistry

Background:

• The Grassmann interpolation (G-Int) method offers efficient density matrix interpolation.
• Spin-unrestricted open-shell systems require separate interpolation for alpha and beta spin density matrices.

Purpose of the Study:

• To extend and evaluate the performance of the G-Int method for spin-unrestricted open-shell systems.
• To assess the utility of G-Int density matrices as initial guesses for self-consistent field (SCF) calculations.
• To explore the direct calculation of atomic charges using G-Int density matrices.

Main Methods:

• Application of G-Int to spin-unrestricted open-shell systems, specifically CO●+ and nickelocene.
• Comparison of G-Int performance against conventional SCF guess schemes.
• Direct calculation of atomic charges using Mulliken and ChElPG population analyses with G-Int density matrices.

Main Results:

• The Frobenius norm errors for alpha and beta spin density matrices were found to be comparable.
• G-Int density matrices significantly outperformed conventional SCF guess schemes.
• Direct SCF energy evaluation without iterations is possible with G-Int density matrices, depending on accuracy requirements.
• First-time use of spin-unrestricted G-Int density matrices for direct atomic charge calculations.

Conclusions:

• The extended G-Int method is effective for spin-unrestricted open-shell systems.
• G-Int provides superior initial guesses for SCF calculations, enhancing computational efficiency.
• The method enables direct calculation of atomic charges, expanding its applicability in electronic structure analysis.