Spin-Free Exact Two-Component Linear Response Coupled Cluster Theory for the Estimation of Frequency-Dependent...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular properties like polarizability is essential in chemistry.
• Relativistic effects become significant for heavy atoms, complicating calculations.
• Existing methods may be computationally expensive or lack accuracy for these systems.

Purpose of the Study:

• To present the theory, implementation, and benchmark results of a new computational method.
• To calculate static and dynamic polarizabilities of atoms and molecules.
• To assess the accuracy and efficiency of the developed method.

Main Methods:

• Development and application of the one-electronic variant of spin-free exact two-component (SFX2C1e) linear response coupled cluster (LRCCSD) theory.
• Utilized the resolution of identity (RI) approximation to reduce computational cost.
• Employed the spin-summed formulation for calculations.

Main Results:

• The SFX2C1e-LRCCSD method was successfully implemented and benchmarked.
• Calculated static and dynamic polarizabilities showed excellent agreement with more rigorous methods (X2C-LRCCSD) and experimental data.
• The RI approximation was found to have a negligible impact on accuracy.

Conclusions:

• The SFX2C1e-LRCCSD theory provides an accurate and efficient approach for calculating polarizabilities.
• Accurate polarizability predictions, especially for heavy atoms, necessitate large basis sets with diffuse functions, electron correlation, and relativistic effects.
• This method offers a valuable tool for studying electronic properties of diverse chemical systems.