Nonadiabatic Molecular Dynamics by Multiconfiguration Pair-Density Functional Theory.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Multireference electronic structure methods are crucial for accurately describing chemical systems with complex electronic structures.
• Existing methods like CASPT2 offer high accuracy but are computationally expensive for dynamics simulations.
• There is a need for more efficient yet accurate methods to study nonadiabatic processes.

Purpose of the Study:

• To implement and validate multiconfiguration pair-density functional theory (MC-PDFT) for ab initio molecular dynamics.
• To introduce MC-PDFT analytical gradients into the SHARC program for nonadiabatic dynamics.
• To assess the performance of MC-PDFT compared to CASPT2 and experimental data.

Main Methods:

• Development of MC-PDFT analytical gradients.
• Integration of MC-PDFT into the SHARC molecular dynamics program.
• Ab initio nonadiabatic molecular dynamics simulations.
• Intersystem crossing dynamics study of thioformaldehyde.

Main Results:

• Successful implementation of MC-PDFT for ab initio molecular dynamics.
• MC-PDFT provides accuracy comparable or superior to CASPT2 at a lower computational cost.
• Excellent agreement observed with CASPT2 and experimental results for thioformaldehyde intersystem crossing.
• Enabled dynamics simulations for larger active spaces (12 electrons in 10 orbitals) previously inaccessible with CASPT2.

Conclusions:

• MC-PDFT is a viable and efficient alternative to CASPT2 for ab initio molecular dynamics.
• The developed method significantly reduces the computational cost of accurate electronic structure calculations for dynamics.
• MC-PDFT opens new possibilities for studying complex chemical dynamics in larger systems.