Evaluation of Spin-Orbit Couplings with Linear-Response Time-Dependent Density Functional Methods.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Spin-orbit coupling (SOC) is crucial for understanding photophysical processes and reaction mechanisms in molecules.
• Accurate calculation of SOC elements is essential for predicting molecular properties and designing new materials.
• Existing methods for SOC calculation can be computationally expensive or limited in applicability.

Purpose of the Study:

• To develop a versatile and efficient computational tool for calculating spin-orbit coupling (SOC) elements.
• To provide an easy-to-use code interfaced with widely used quantum chemistry packages.
• To benchmark the accuracy and reliability of the developed code against established methods.

Main Methods:

• Development of a Python-based code named PySOC.
• Interfacing PySOC with quantum chemistry packages like Gaussian 09 and DFTB+.
• Utilizing linear-response (LR) methods within time-dependent density functional theory (TDDFT), Tamm-Dancoff approximation (TDA), and time-dependent density functional tight binding (TD-DFTB).
• Employing Casida-type wave functions and the Breit-Pauli (BP) spin-orbit Hamiltonian with an effective charge approximation.

Main Results:

• PySOC successfully calculates SOC elements between singlet and triplet states for various organic molecules.
• Computed SOC values show minimal basis set dependence but are sensitive to the choice of density functional.
• Benchmark results demonstrate good agreement with reference data from higher-level methods like CASPT2 and DFT/MRCI.

Conclusions:

• PySOC offers a versatile and accurate approach for calculating SOC elements.
• The code's modular design allows for easy integration with other computational chemistry packages and methods.
• PySOC provides a valuable tool for researchers investigating SOC effects in molecular systems.