Implementation and Validation of Constrained Density Functional Theory Forces in the CP2K Package.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Condensed matter physics

Background:

• Constrained density functional theory (CDFT) is valuable for simulating electron transfer parameters in condensed phases.
• Existing CDFT methods in CP2K utilize Becke partitioning, which can yield unphysical atomic charges.
• There is a need for improved partitioning schemes in CDFT for greater accuracy.

Purpose of the Study:

• To implement and verify an extension of CDFT in the CP2K package using Hirshfeld charge partitioning.
• To improve the accuracy of atomic charge calculations in CDFT by replacing the Becke partitioning scheme.
• To assess the computational efficiency and reliability of the new CDFT implementation for condensed phase systems.

Main Methods:

• Extension of the Constrained Density Functional Theory (CDFT) methodology within the CP2K software package.
• Implementation of force terms derived from Hirshfeld charge partitioning for constraint application.
• Validation of the new implementation through simulations of electron transfer in (H2O)2+, electron tunneling in MgO, and electron self-exchange in aqueous Ru complexes.

Main Results:

• The Hirshfeld-based CDFT implementation in CP2K successfully reproduces electron transfer parameters.
• The new method avoids the unphysical atomic charges associated with the Becke partitioning scheme.
• Simulations using the extended CDFT show good agreement with prior plane-wave CDFT results.

Conclusions:

• The Hirshfeld-based CDFT extension in CP2K provides a computationally efficient and reliable approach for condensed phase electron transfer studies.
• This improved CDFT method enhances the accuracy of atomic charge partitioning, leading to more physically realistic simulation results.
• The study confirms the general reliability of condensed phase CDFT calculations with the enhanced partitioning scheme.