Spin Dynamics of\nRadical Pairs Using the Stochastic\nSchrodinger Equation in <i>MolSpin</i>

The chemical reactivity of radical pairs is strongly\ninfluenced\nby the interactions of electronic and nuclear spins. A detailed understanding\nof these effects requires a quantum description of the spin dynamics\nthat considers spin-dependent reaction rates, interactions with external\nmagnetic fields, spin–spin interactions, and the loss of spin\ncoherence caused by coupling to a fluctuating environment. Modeling\nreal chemical and biochemical systems, which frequently involve radicals\nwith multinuclear spin systems, poses a severe computational challenge.\nHere, we implement a method based on the stochastic Schrödinger\nequation in the software package <i>MolSpin</i>. Large electron–nuclear\nspin systems can be simulated efficiently, with asymmetric spin-selective\nrecombination reactions, anisotropic hyperfine interactions, and nonzero\nexchange and dipolar couplings. Spin-relaxation can be modeled using\nthe stochastic time-dependence of spin interactions determined by\nmolecular dynamics and quantum chemical calculations or by allowing\nrate coefficients to be explicitly time-dependent. The flexibility\nafforded by this approach opens new avenues for exploring the effects\nof complex molecular motions on the spin dynamics of chemical transformations.