First-principes study of G center using CDFT and TDDFT with forces

Isolated point defects in semiconductors that emit in the telecom wavelengths hold promise for building networks of photonically coupled qubits. The G center is a complex defect in silicon with a C-Si-C configuration. It emits brightly near the telecom O-band, with a metastable triplet state that offers potential for quantum memory. In this talk, we will discuss the first-principles simulation of electronic structures of the G center. We employed both constrained DFT (CDFT) method and TDDFT with analytical forces to simulate the excited-state electronic and atomic structures. We benchmarked how these methods predict the optical and phononic properties using the G center as a study case. Our work highlights the advantages of TDDFT with forces for studying quantum defects with complex electronic structures and propose practical considerations when applying constrained DFT methods.