Beyond the method chosen for the dynamics, the main determination of computational cost for NAMD is the electronic structure calculations of the ground and excited state gradients as well as the nonadiabatic coupling (NAC) vectors. For many NAMD simulations of bond-breaking reactions, a multi-reference method such as state-averaged complete active space self-consistent field (SA-CASSCF) or CAS with configuration interaction (CAS-CI) is employed. In other nonadiabatic processes more affordable single reference excited state methods such as linear response time-dependent density functional theory (TDDFT) are used. TDDFT, especially when employing a long-range corrected hybrid functional, often can provide accurate vertical excitation energies near the ground state minimum, but due to its single reference nature will generally poorly describe bond breaking, biradical intermediates, and crossings between ground and excited state potential energy surfaces. TDDFT has recently shown to be accurate in modeling conical intersections between excited states, and variants of excited state single reference methods, e.g. with references with different spin, particle number, or excitation level, have shown promise in capturing nondynamic correlation, but haven't seen widespread use for NAMD simulations.