Forces on nuclei moving on autoionizing molecular potential energy surfaces

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Autoionization is a key process in molecular systems, including biochemical ones.
• Calculating forces on nuclei during autoionization is essential for understanding molecular dynamics and radiation damage.
• Existing methods for molecular dynamics simulations rely on force fields within the Born-Oppenheimer approximation.

Purpose of the Study:

• To develop a method for calculating the real forces on nuclei moving on complex potential energy surfaces (CPESs) during autoionization.
• To investigate the relationship between classical nuclear forces and the CPES during autoionization.
• To understand the implications for radiative damage in biological molecules like RNA and DNA.

Main Methods:

• Utilized a transformation of the time-dependent Schrödinger equation, following Madelung's approach.
• Derived classical forces on nuclei from the real part of the CPES.
• Analyzed the time-dependence of nuclear forces in the context of autoionization decay.

Main Results:

• Demonstrated that classical forces on nuclei correlate with the gradient of the real part of the CPES.
• Showed that forces on nuclei in metastable molecules are time-independent, despite exponential decay in detection probability.
• Established that nuclear forces vary in time due to the autoionization process, irrespective of the potential energy surface.

Conclusions:

• The study provides a theoretical framework for calculating nuclear forces during molecular autoionization.
• This work advances the understanding of electron dynamics and potential energy surfaces in molecular systems.
• The findings have implications for modeling radiation damage in biomolecules and designing new quantum chemistry methods.