We propose an extension to the Davydov D_2 Ansatz in the dynamics study of the Holstein molecular crystal model with diagonal and off-diagonal exciton-phonon coupling using the Dirac-Frenkel time-dependent variational principle. The new trial state by the name of the "multi-D_2 Ansatz" is a linear combination of Davydov D_2 trial states, and its validity is carefully examined by quantifying how faithfully it follows the Schrödinger equation. Considerable improvements in accuracy have been

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... trated in comparison with the usual Davydov trial states, i.e., the single D_1 and D_2 Ansätze. With an increase in the number of the Davydov D_2 trial states in the multi-D_2 Ansatz, deviation from the exact Schrödinger dynamics is gradually diminished, leading to a numerically exact solution to the Schrödinger equation.