  The spin coherence times of 69 triplet defect centers in 45 different 2D host
materials are calculated using the cluster correlation expansion (CCE) method
with parameters of the spin Hamiltonian obtained from density functional theory
(DFT). Several of the triplets are found to exhibit extraordinarily large spin
coherence times making them interesting for quantum information processing. The
dependence of the spin coherence time on various factors, including the
hyperfine coupling strength, the dipole-dipole coupling, and the nuclear
g-factors, are systematically investigated. The analysis shows that the spin
coherence time is insensitive to the atomistic details of the defect center and
rather is dictated by the nuclear spin properties of the host material.
Symbolic regression is then used to derive a simple expression for spin
coherence time, which is validated on a test set of 55 doublet defects unseen
by the regression model. The simple expression permits order-of-magnitude
estimates of the spin coherence time without expensive first principles
calculations.
