ReSpect: Relativistic spectroscopy DFT program package.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Growing interest in compounds with heavier elements necessitates advanced computational methods.
• Existing methods struggle to simultaneously address relativistic, spin-polarization, and electron correlation effects efficiently.

Purpose of the Study:

• Introduce the ReSpect program for efficient relativistic DFT calculations.
• Detail the theoretical and technical advancements enabling its performance.
• Demonstrate its capability in predicting molecular and solid-state properties.

Main Methods:

• Utilizes quasirelativistic two-component (X2C) and fully relativistic four-component (Dirac-Coulomb) DFT.
• Incorporates Kramers-unrestricted self-consistent field for spin polarization in open-shell systems.
• Employs efficient algorithms leveraging time-reversal symmetry, biquaternion algebra, and localized Gaussian-type orbitals.

Main Results:

• ReSpect handles molecules with >100 atoms at the four-component level efficiently on standard CPU clusters.
• Computational cost is often within a factor of 10 of non-relativistic calculations.
• Accurate prediction of diverse spectroscopic parameters (EPR, NMR, optical properties) and band structures.

Conclusions:

• ReSpect provides a computationally feasible approach for studying relativistic effects in heavy-element systems.
• The program facilitates accurate prediction of a wide range of molecular and solid-state properties.
• Enables advanced simulations including real-time TDDFT electron dynamics.