First -principles simulation of spin-phonon coupling in Cr(otolyl)₄

Relaxation dynamics fundamentally determine the practical utility of molecular qubits. In particular, the spin–lattice relaxation time (T₁) governs vibrationally mediated decoherence processes and defines how long a molecular spin can retain its initialized state before returning to thermal equilibrium after excitation. Previous experimental studies have highlighted S = 1 molecular color centers such as Cr(otolyl)₄, which can be optically initialized, coherently manipulated with microwaves, and exhibit T₁ times longer than their optical emission lifetimes.

In this work, we employ first-principles simulations to investigate spin–phonon coupling in molecular color centers, using Cr(otolyl)₄ as a benchmark system. We combined complete active space methods for accurate spin description with solid-state density functional perturbation theory to describe lattice vibrations. We analyze how key molecular and vibrational parameters influence the spin–lattice relaxation time, providing microscopic insight into the mechanisms governing spin relaxation in optically addressable molecular qubits.