Parameters for excess electron transfer in DNA. Estimation using unoccupied Kohn-Sham orbitals and TD DFT

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Accurate estimation of excess electron transfer (EET) parameters is crucial for understanding charge transport in molecular systems.
• Traditional methods for calculating EET parameters can be computationally intensive and may involve approximations for radical anions.
• The electronic structure of pi stacks, particularly in nucleobases, plays a significant role in charge transport phenomena.

Purpose of the Study:

• To investigate the efficacy of using unoccupied Kohn-Sham orbitals (UKSO) from neutral pi stacks for estimating excess electron transfer (EET) energetics and electronic couplings.
• To compare the performance of various Density Functional Theory (DFT) functionals in predicting EET parameters using the UKSO approach.
• To evaluate the accuracy of the UKSO method against established multi-state perturbation theory (MS-PT2) calculations.

Main Methods:

• Density Functional Theory (DFT) calculations were performed using SVWN, BP86, BLYP, B3LYP, and BH&HLYP functionals.
• Unoccupied Kohn-Sham orbitals (UKSO) of neutral pi stacks were utilized to estimate EET parameters.
• Multi-state perturbation theory (MS-PT2) results for seven nucleobase pi stacks served as reference data.
• Time-Dependent DFT (TD DFT) calculations were also performed for comparison.

Main Results:

• The UKSO approach, particularly with B3LYP and SVWN functionals, provided accurate estimations of EET energetics and electronic couplings.
• UKSO calculations showed good agreement with MS-PT2 reference data for the studied pi stacks.
• TD DFT calculations yielded less accurate EET parameters compared to the UKSO method.
• The Lowest Unoccupied Molecular Orbitals (LUMOs) of neutral systems effectively described excess charge distribution in radical anions.
• Spin-unrestricted DFT calculations of radical anions tended to overestimate electron delocalization.

Conclusions:

• The UKSO method offers an efficient and accurate strategy for calculating EET parameters in DNA pi stacks by utilizing calculations on neutral systems.
• The B3LYP and SVWN DFT functionals demonstrate superior performance within the UKSO approach for EET parameter estimation.
• UKSO calculations provide a reliable alternative to more computationally demanding methods for assessing charge transport properties.