Finite-temperature coupled cluster: Efficient implementation and application to prototypical systems

Area of Science:

• Computational chemistry
• Quantum mechanics
• Materials science

Background:

• Accurate theoretical descriptions of systems at finite temperatures are crucial for understanding materials under extreme conditions.
• Existing methods often struggle to balance accuracy and computational cost for correlated systems at elevated temperatures.

Purpose of the Study:

• To present the theory and implementation of the finite temperature coupled cluster singles and doubles (FT-CCSD) method.
• To assess the numerical aspects and practical application guidelines for FT-CCSD.
• To apply FT-CCSD to model systems and the uniform electron gas (UEG) under warm, dense conditions.

Main Methods:

• Development and implementation of the FT-CCSD equations for response properties.
• Numerical testing involving orbital space truncation and amplitude equation integration.
• Application to the 1D Hubbard model, UEG, and simple materials.

Main Results:

• FT-CCSD provides a qualitatively accurate description of finite-temperature correlation effects in the 1D Hubbard model, even at strong interactions (U=8).
• The method enables systematic computation of exchange-correlation energies for the warm, dense UEG across various conditions.
• Encouraging performance observed for model systems at high temperatures.

Conclusions:

• FT-CCSD is a promising method for studying finite-temperature correlation effects in condensed matter systems.
• The method offers a pathway to systematically improvable electronic structure calculations for warm, dense matter.
• Further development is needed to overcome obstacles for applying FT-CCSD to realistic ab initio materials calculations.