Parameterized Bases for Calculating Vibrational Spectra Directly from ab Initio Data Using Rectangular Collocation.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Calculating anharmonic vibrational spectra is crucial for understanding molecular behavior.
• Existing methods often require complex potential energy functions.
• Efficient computation of vibrational energy levels is an ongoing challenge.

Purpose of the Study:

• To compare different parametrized basis sets for computing anharmonic vibrational spectra.
• To evaluate a new version of the rectangular collocation-optimization method.
• To determine optimal basis sets for ultrasmall basis computations.

Main Methods:

• Utilized a novel rectangular collocation-optimization method.
• Employed parametrized uncoupled and coupled Gaussian functions.
• Tested direct-product and coupled Hermite basis sets.
• Computed vibrational energy levels for H2O using model potential energy surfaces and ab initio points.

Main Results:

• Successfully computed low-lying vibrational energy levels with an ultrasmall basis set.
• Demonstrated the method's ability to bypass the need for a potential function.
• Identified uncoupled parametrized Gaussian and Hermite functions as effective for anharmonic and coupled systems.

Conclusions:

• Uncoupled parametrized Gaussian and Hermite basis sets are well-suited for anharmonic and coupled vibrational problems.
• The collocation-optimization method offers an efficient route to vibrational spectra computation.
• This approach simplifies the calculation of molecular vibrational properties.