Finding Excited-State Minimum Energy Crossing Points on a Budget: Non-Self-Consistent Tight-Binding Methods.

Area of Science:

• Computational Chemistry
• Photochemistry
• Quantum Mechanics

Background:

• Studying photochemical processes requires identifying minimum energy conical intersections (MECIs).
• Calculating non-adiabatic derivative coupling vectors for MECIs is computationally intensive.
• Minimum energy crossing points (MECPs) offer a computationally feasible alternative.

Purpose of the Study:

• To develop a simplified and efficient computational method for identifying MECPs.
• To enable the study of photochemical processes by facilitating the exploration of crossing points between diabatic states.

Main Methods:

• A simplified treatment using the non-self-consistent extended tight-binding method, GFN0-xTB.
• Calculation of energies and gradients for multiple electronic states via a single Hamiltonian diagonalization.
• A derivative coupling-vector-free scheme for MECP calculation.

Main Results:

• The GFN0-xTB method provides energies and gradients for multiple electronic states efficiently.
• Identified MECP geometries serve as effective starting points for refinement.
• Comparison with high-lying MECIs of benchmark systems validates the approach.

Conclusions:

• The presented GFN0-xTB method offers a computationally advantageous route to MECPs.
• This method simplifies the study of photochemical reaction pathways.
• The identified geometries are valuable for subsequent high-accuracy ab initio calculations.