Hybrid Optimized and Localized Vibrational Coordinates.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Standard normal coordinates (NCs) can be computationally intensive for vibrational structure calculations.
• Optimized Coordinates (OCs) and Localized Coordinates (LCs) offer improvements but have limitations.
• Efficient vibrational structure calculations are crucial for understanding molecular properties.

Purpose of the Study:

• To develop a new set of rectilinear vibrational coordinates, Hybrid Optimized and Localized Coordinates (HOLCs).
• To enable fast convergence in vibrational structure calculations.
• To provide a computationally efficient and accurate method for anharmonic energy calculations.

Main Methods:

• HOLCs are derived by optimizing vibrational self-consistent field (VSCF) energy with a penalty for delocalization.
• The method utilizes orthogonal transformations and a localization measure.
• The same theoretical framework and implementation cover OCs, LCs, and HOLCs.

Main Results:

• HOLCs demonstrate fast convergence and accurate vibrational anharmonic energies, comparable to OCs.
• Surprisingly good results are achieved using HOLCs with simple quadratic Taylor expansions of potential energy surfaces.
• HOLCs are computationally less demanding than OCs for larger molecular systems.

Conclusions:

• HOLCs offer a pragmatic and efficient alternative for anharmonic calculations on medium to large molecular systems.
• The method provides a balance between the benefits of OCs and LCs.
• HOLCs facilitate accurate vibrational structure calculations with reduced computational cost.