Finite Temperature Coupled Cluster Theories for Extended Systems.

Area of Science:

• Quantum chemistry
• Materials science
• Computational physics

Background:

• Coupled cluster theories are standard for zero-temperature electronic property predictions.
• Zero-temperature approximations fail for small band gap systems like metals.
• Thermal effects significantly influence chemistry on metal surfaces.

Purpose of the Study:

• To develop a coupled cluster method that accurately accounts for thermal effects in electronic systems.
• To enable efficient computation of electronic properties at finite temperatures, including room temperature.
• To investigate the thermal behavior of metallic and semiconducting materials.

Main Methods:

• A novel coupled cluster implementation in the imaginary time domain [0, β].
• Solution of imaginary time-dependent coupled cluster amplitude integral equations.
• Linearized direct ring doubles approximation (Tamm-Dancoff approximation with screened exchange).

Main Results:

• The new method allows a uniform transition from finite to zero temperature calculations without added cost.
• Accurate calculations are feasible down to room temperature.
• Correlation grand potentials were computed for solid lithium (metal) and solid silicon (semiconductor) across various temperatures.

Conclusions:

• The developed imaginary time-domain coupled cluster method provides an efficient and accurate way to study temperature-dependent electronic properties.
• This approach is particularly valuable for metallic systems where thermal effects are significant.
• The study demonstrates the method's applicability to real materials like lithium and silicon.