Analytical nonadiabatic coupling and state-specific energy gradient for the crystal field Hamiltonian describing lanthanide single-ion magnets

Abstract

Paramagnetic molecules with a metal ion as an electron spin center are promising building blocks for molecular qubits and high-density memory arrays. However, fast spin relaxation and decoherence in these molecules lead to a rapid loss of magnetization and quantum information. Nonadiabatic coupling (NAC), closely related to spin-vibrational coupling, is the main source of spin relaxation and decoherence in paramagnetic molecules at higher temperatures. Predicting these couplings using numerical differentiation requires a large number of computationally intensive ab initio or crystal field electronic structure calculations. To reduce computational cost and improve accuracy, we derive and implement analytical NAC and state-specific energy gradient for the ab initio parametrized crystal field Hamiltonian describing single-ion molecular magnets. Our implementation requires only a single crystal field calculation. In addition, the accurate NACs and state-specific energy gradients can be used to model spin relaxation using sophisticated nonadiabatic molecular dynamics, which avoids the harmonic approximation for molecular vibrations. To test our implementation, we calculate the NAC values for three lanthanide complexes. The predicted values support the relaxation mechanisms reported in previous studies.

Dissociation Time, Quantum Yield, and Dynamic Reaction Pathways in the Thermolysis of trans-3,4-Dimethyl-1,2-dioxetane

“…The enhancement of the quantum yields of singlet and triplet chemiexcitation was achieved experimentally by the methylation of the 1,2-dioxetanes. , The chemiluminescent mechanism has been studied by computing potential energy surface (PESs), locating minima, transition states (TSs), and conical interactions and/or intersystem crossings, and identifying the potential reaction pathways. − The dynamical quantities, e.g., dissociation time and branching ratios, however, cannot be analyzed in the context of critical points and PESs. The high demand for the nonadiabatic molecular dynamics (NAMD) methods, in which the nuclear motion is regulated by multiple electronic states, has led to the development of different approaches. − As the full quantum-mechanical methods are expensive and limited to a few degrees of freedom, − the trajectory surface hopping (TSH) method has emerged as one of the most popular tools for the NAMD simulations, which was used recently to study the chemiluminescent processes for the four-membered heterocyclic peroxides …”