Automated Many-Body Analysis of Point Defects

Sammanfattning

Point defects in crystals have been shown to be useful as building blocks for quantum technology. In the search for new defects with properties better suited for specific applications, a detailed understanding of their many-body state structure is needed. Accurately modeling the states cannot be done using standard density functional theory (DFT) methods, and true many-body methods are computationally expensive. We develop a general computational tool for constructing many-body defect states, and for estimating their energies from constrained occupation DFT calculations. The tool is used to construct configuration state functions (CSF) for active spaces of orbitals in any of the 32 point groups. The CSF were constructed for several defects, and the results agree with states reported in the literature. The many-body energies are estimated by first expressing single-determinant energies as linear combinations of the unknown CSF energies and then solving the resulting system of equations. We applied this method to estimate the many-body energies for the nitrogen-vacancy (NV) center and the sodium substitution in diamond. For the NV center, the ordering of CSF energies was found to be sensitive to the specific DFT settings. The many-body states of the sodium substitution in diamond have not been mapped out previously; we present them here. The developed tool simplifies complex group-theory calculations, enabling the mapping of excited states of numerous point defects, potentially offering a cheaper alternative to true many-body methods for high-throughput screening of candidates for quantum technology.