A static quantum embedding scheme based on coupled cluster theory.

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• Coupled Cluster (CC) theory provides high accuracy but is computationally expensive.
• Quantum embedding methods aim to reduce computational cost by treating different parts of a system with varying levels of theory.
• Previous hybrid methods have combined Møller-Plesset (MP) and CC approaches with limitations.

Purpose of the Study:

• To develop a novel static quantum embedding scheme, termed MP-CC.
• To efficiently compute molecular properties by combining high-level CC for an active fragment and lower-level MP for the environment.
• To improve upon existing hybrid MP-CC methods by targeting specific molecular fragments and introducing environmental relaxation mechanisms.

Main Methods:

• Developed a static quantum embedding scheme (MP-CC).
• Employed high-level CC theory for the active fragment and lower-level MP perturbation for the environment.
• Incorporated orbital relaxation in the environment for enhanced accuracy.
• Utilized localized bonds as active fragments for studying bond breaking and torsion.

Main Results:

• MP-CC demonstrated effectiveness on potential energy curves and thermochemical reaction energies.
• Orbital relaxation in the environment significantly improved results.
• Accurate calculations for N=N bond breaking in azomethane and C-C bond torsion in butadiene were achieved.
• Accuracy improved with increasing fragment Hilbert space size, approaching full CC precision.

Conclusions:

• The MP-CC method offers a computationally efficient yet accurate approach for quantum chemical calculations.
• Orbital relaxation and fragment Hilbert space size are crucial for achieving high accuracy.
• MP-CC provides a promising framework for studying complex chemical systems.