  We describe and extend the formalism of state-specific analytic density
matrix renormalization group (DMRG) energy gradients, first used by Liu et al
(J. Chem. Theor.Comput. 9, 4462 (2013)). We introduce a DMRG wavefunction
maximum overlap following technique to facilitate state-specific DMRG excited
state optimization. Using DMRG configuration interaction (DMRG-CI) gradients we
relax the low-lying singlet states of a series of trans-polyenes up to C20H22.
Using the relaxed excited state geometries as well as correlation functions, we
elucidate the exciton, soliton, and bimagnon ("single-fission") character of
the excited states, and find evidence for a planar conical intersection.

Chemical Physics