Time-dependent optimized coupled-cluster method with doubles and perturbative triples for first principles simulation...

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Physics

Background:

• Accurate simulation of multielectron dynamics in intense laser fields is crucial for understanding atomic and molecular responses.
• Existing methods like TD-CASSCF and TD-OCCD(T) have limitations in accuracy or computational cost.
• The development of efficient and accurate theoretical frameworks is essential for first-principles simulations.

Purpose of the Study:

• To introduce a new, cost-effective approximation method, TD-OCCD(T), within the time-dependent optimized coupled-cluster (TD-OCC) framework.
• To extend the accuracy of the ground-state CCSD(T) method to time-dependent electronic structure calculations.
• To provide a reliable tool for simulating the dynamics of multielectron systems interacting with intense laser fields.

Main Methods:

• Formulation of the time-dependent, orbital-optimized TD-OCCD(T) method based on the real-valued time-dependent variational principle.
• Derivation of equations of motion for orbital functions and coupled-cluster amplitudes using a fourth-order Lagrangian.
• Implementation and application of the TD-OCCD(T) method for simulating strong-field ionization and high-order harmonic generation.

Main Results:

• The TD-OCCD(T) method is shown to be size extensive and gauge invariant.
• The computational scaling of the method is determined to be O(N^7) with respect to the number of active orbitals (N).
• Pilot applications to Krypton (Kr) atom demonstrate the method's capability in reproducing strong-field phenomena.

Conclusions:

• The developed TD-OCCD(T) method offers a cost-effective and accurate approach for first-principles simulations of multielectron dynamics.
• TD-OCCD(T) provides a valuable alternative to existing methods, potentially improving the accuracy and efficiency of simulations.
• This advancement facilitates deeper insights into light-matter interactions and related phenomena in atomic systems.