Vibrational multiconfiguration self-consistent field theory: implementation and test calculations.

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy

Background:

• Accurate prediction of molecular vibrational spectra is crucial for understanding molecular properties and dynamics.
• Traditional methods often struggle with the complexity of anharmonic effects in vibrational spectra.

Purpose of the Study:

• To introduce a novel state-specific vibrational multiconfiguration self-consistent field (VMCSCF) approach.
• To enable accurate calculations of anharmonic vibrational spectra.
• To evaluate the performance of the VMCSCF method and its variant, vibrational complete active space self-consistent field (VCASSCF).

Main Methods:

• Utilizing a multimode expansion of the potential energy surface.
• Implementing a state-specific VMCSCF approach.
• Discussing VCASSCF as a specialized case.

Main Results:

• The developed VMCSCF approach provides accurate anharmonic vibrational spectra.
• VCASSCF calculations demonstrate superior convergence compared to the general VMCSCF approach.
• Benchmark calculations on small molecules validate the method's efficacy.

Conclusions:

• The state-specific VMCSCF method is a powerful tool for anharmonic vibrational spectra.
• VCASSCF is the preferred multiconfigurational approach due to its convergence properties.
• This methodology advances computational spectroscopy for molecular analysis.