Vibrational absorption spectra calculated from vibrational configuration interaction response theory using the...

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Mechanics

Background:

• Vibrational response functions are crucial for understanding molecular properties.
• Calculating these functions often requires extensive computational resources, limiting analysis to specific frequency ranges.
• Existing methods may necessitate converging all vibrational eigenstates, which is computationally demanding.

Purpose of the Study:

• To present an efficient Lanczos method for computing linear vibrational response functions across arbitrary frequency intervals.
• To demonstrate how the complex part of the response function yields the absorption spectrum.
• To show that global spectral information can be obtained without converging all eigenstates.

Main Methods:

• Application of the Lanczos method to compute linear vibrational response functions.
• Analysis of the imaginary component of the response function to obtain absorption spectra.
• Construction of a tridiagonal Lanczos matrix, which is built only once per operator.

Main Results:

• The Lanczos method efficiently provides the complete linear vibrational response function over any frequency range.
• The method successfully yields absorption spectra from the response function.
• Global spectral information is accessible without the need to converge all vibrational eigenstates.
• Example calculations for cyclopropene and uracil validate the method's efficacy.

Conclusions:

• The Lanczos method offers an efficient and robust approach for calculating vibrational absorption spectra.
• This technique provides a global view of the spectrum, overcoming limitations of methods requiring full eigenstate convergence.
• The presented method is applicable to various molecular systems, as demonstrated by the cyclopropene and uracil examples.