Linear Scaling Constrained Density Functional Theory in CONQUEST.

Area of Science:

• Computational chemistry
• Materials science
• Biophysics

Background:

• Density functional theory (DFT) is a powerful tool for electronic structure calculations.
• Simulating electron-transfer processes in large systems is computationally challenging.
• Existing DFT methods may struggle with accuracy for large, complex systems.

Purpose of the Study:

• To implement and validate the constrained density functional theory (cDFT) formalism in the CONQUEST code.
• To enable efficient simulations of electron-transfer processes in large biological and technological systems.
• To assess the accuracy and applicability of cDFT for various molecular systems.

Main Methods:

• Implementation of cDFT within the linear scaling DFT code CONQUEST.
• Utilizing the Becke weight population scheme for constraint definition.
• Analytical and efficient calculation of force components in a linear scaling framework.
• Demonstration calculations on biphenyl molecules, poly(phenylene-vinylene) oligomers, and a hydrated DNA 10-mer.

Main Results:

• The cDFT implementation is compatible with density matrix truncation.
• Accurate energy and geometry changes were obtained for charge-separated excited states in biphenyl molecules.
• Successful application of cDFT to larger systems, including oligomers and DNA fragments.
• Validation of the method's capability for simulating electron transfer in complex systems.

Conclusions:

• The implemented cDFT formalism provides an accurate and efficient method for studying electron-transfer processes.
• This approach extends the applicability of DFT to larger and more complex biological and technological systems.
• The cDFT method shows significant promise for advancing research in areas involving charge transfer phenomena.