Local Excitations of a Charged Nitrogen Vacancy in Diamond with Multireference Density Matrix Embedding Theory

Area of Science:

• Quantum Computing
• Materials Science
• Solid-State Physics

Background:

• The negatively charged nitrogen-vacancy (NV-) center in diamond is a promising qubit for quantum computing.
• Accurate theoretical descriptions of its excited states are crucial for understanding its properties.
• Previous methods struggled with the strong electron correlation in NV- systems.

Purpose of the Study:

• To investigate the electronic structure and excitation energies of the NV- center in diamond.
• To apply and validate periodic density matrix embedding theory (pDMET) for charged periodic systems.
• To benchmark the performance of CASSCF/NEVPT2 as an impurity solver within pDMET.

Main Methods:

• Utilized periodic density matrix embedding theory (pDMET) for a periodic supercell model of the NV- center.
• Employed complete active space self-consistent field (CASSCF) and n-electron valence state second-order perturbation theory (NEVPT2) as the impurity solver.
• Performed linear regression extrapolation of excitation energies to the non-embedding limit.

Main Results:

• Achieved excellent agreement between extrapolated NEVPT2-DMET excitation energies and experimental values.
• Obtained a first triplet-triplet excitation energy of 2.31 eV and a singlet-singlet transition energy of 1.02 eV.
• Demonstrated the successful application of pDMET to a charged periodic system.

Conclusions:

• The combination of pDMET and NEVPT2 provides an accurate and reliable method for studying NV- centers.
• This approach overcomes limitations of previous methods for strongly correlated excited states.
• The study validates pDMET for charged periodic systems and advances the theoretical understanding of the NV- defect.