Large-Scale Modeling of Proton-Coupled Electron Transfer Based on Block-Localized Kohn-Sham Orbitals.

Area of Science:

• Quantum chemistry
• Theoretical chemistry
• Computational chemistry

Background:

• Proton-coupled electron transfer (PCET) reactions are crucial in biological processes.
• Calculating PCET reaction rate constants is computationally demanding, often requiring multireference methods like CASSCF.
• Existing methods face scalability limitations for large molecular systems.

Purpose of the Study:

• To develop computationally efficient and scalable methods for calculating PCET reaction rate constants.
• To investigate the efficacy of multistate density-functional theory (MS-DFT) with block-localized Kohn-Sham (BLKS) orbitals as an alternative to CASSCF.
• To assess the accuracy of vibronic coupling calculations using different operators for BLKS orbital construction.

Main Methods:

• Utilized multistate density-functional theory (MS-DFT) with block-localized Kohn-Sham (BLKS) orbitals.
• Investigated various operators for constructing BLKS orbitals.
• Compared results with complete active space self-consistent field (CASSCF) and N-electron valence state second-order perturbation theory (NEVPT2).
• Applied the method to a DNA-acrylamide complex, including spectator fragments.

Main Results:

• Accurate vibronic couplings were obtained using a non-Hermitian operator for BLKS construction.
• The MS-DFT/BLKS method demonstrated good agreement with CASSCF and NEVPT2.
• The fragmentation approach of BLKS allowed for the inclusion of spectator fragments at a manageable computational cost.
• Successful application to a complex system like DNA-acrylamide.

Conclusions:

• MS-DFT with BLKS orbitals provides a scalable and accurate approach for calculating PCET reaction rate constants.
• The use of a non-Hermitian operator enhances the accuracy of vibronic coupling calculations.
• This method offers a promising alternative for studying large molecular systems relevant to biological processes.