Reduced Basis Set Dependence in Anharmonic Frequency Calculations Involving Localized Coordinates.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Localized normal coordinates simplify nuclear Hamiltonians, speeding up anharmonic frequency calculations.
• Atomic displacements in localized coordinates minimally impact electronic structure, offering potential for computational savings.

Purpose of the Study:

• Investigate methods to enhance computational efficiency in ab initio electronic structure calculations.
• Explore strategies for reducing basis set dependence in potential energy surface calculations.

Main Methods:

• Examined three schemes for reducing basis set dependence: localized coordinates with mixed basis sets, distance-based force-field reductions, and coordinate-specific basis sets.
• Analyzed the impact of localized coordinates on electronic structure and interactions.

Main Results:

• Localized normal coordinates effectively reduce the complexity of nuclear Hamiltonians and wave functions.
• Basis set dependence was successfully reduced using the investigated schemes.
• The significance of accurately describing electronic interactions decreases for remote atom displacements and interactions.

Conclusions:

• Localized normal coordinates offer a viable strategy for accelerating anharmonic frequency calculations.
• Combining localized coordinates with reduced basis sets presents an efficient approach for ab initio electronic structure calculations.
• Computational cost can be significantly reduced by exploiting the diminishing importance of electronic interactions for remote atoms.