Semistochastic Heat-Bath Configuration Interaction and Coulomb Truncation for Quantum Defect Embedding Theory in Wide-Bandgap Semiconductors

Solid-state point defects have been considered as promising candidates for spin qubits in quantum sensing and communication applications. Accurate description of their excited-states is essential for obtaining reliable optical and spin properties. Quantum defect embedding theory (QDET) can treat the active space relevant to defects with full electron correlation and the environment solids at the GW approximation [1]. Achieving convergence of the vertical excitation energies within QDET, particularly when including conduction states, remains challenging because of their high computational cost.

Here, we employed the stochastic heat-bath configuration interaction (SHCI) approach to accelerate the active space convergence, enabling convergence of both occupied and unoccupied levels with dozens of electrons efficiently [2].  Furthermore, we discuss our implementation of state overlap functions for reliable state identification across different active spaces. We tested this approach on NV center, SiV0, and Fe in AlN, demonstrating reliable convergence of their vertical excitation energies. Finally, for two-dimensional wide-bandgap semiconductors, we implement Coulomb truncations within the WEST code for both GW-BSE and QDET to significantly improve the vacuum convergence [3].   

[1] S. Chen, et al., J. Chem. Theory Comput. 21, 7797 (2025).

[2] J. Li, et al., J. Chem. Phys. 149, 214110 (2018).

[3] F. Wu, et al., Phys. Rev. Mater. 1, 071001 (2017).