NAST: Nonadiabatic Statistical Theory Package for Predicting Kinetics of Spin-Dependent Processes

Area of Science:

• Chemical Kinetics
• Theoretical Chemistry
• Computational Chemistry

Background:

• Spin-dependent processes, such as intersystem crossings and spin crossovers, are crucial in chemistry and biology.
• Predicting the kinetics of these nonadiabatic processes is computationally challenging.
• Existing methods often struggle with large molecular systems or slow reaction rates.

Purpose of the Study:

• To introduce a new computational package, the Nonadiabatic Statistical Theory (NAST) package.
• To enable accurate prediction of kinetics for spin-dependent processes.
• To provide a versatile tool applicable to large molecular systems and slow nonadiabatic reactions.

Main Methods:

• The NAST package implements a nonadiabatic statistical theory.
• It calculates transition probabilities and rates between electronic states of different spin multiplicities.
• The theory accounts for quantum effects like tunneling and zero-point vibrational energy.

Main Results:

• The NAST package can compute both microcanonical and canonical rate constants.
• It reduces to traditional transition state theory in the adiabatic limit.
• The package requires minimal input data, such as nuclear Hessians and spin-orbit coupling at the minimum energy crossing point (MECP).

Conclusions:

• The NAST package offers an efficient and accurate method for studying spin-dependent chemical kinetics.
• Its ability to handle large systems and incorporate quantum effects makes it valuable for diverse applications.
• The package includes computational tools to facilitate data extraction and advanced calculations.