The time dependent Dirac–Frenkel–McLachlan variation of parameters: An NMR application

[Display omitted] ► Application of the Dirac–Frenkel–McLachlan variation of parameters to NMR. ► Analytical approximations to time dependent problems can be generated. ► Self contained estimate of approximation performance. The time dependent variation of parameters solution to the time dependent Schrödinger equation pioneered by Dirac, Frenkel, and McLachlan is described in terms useful for immediate application to complex time dependent problems in magnetic resonance. A benchmark comparison of the theory to one dimensional images and spin echo envelope signals in simple spatially varying magnetic fields with molecular diffusion is provided.