Evaluating the anharmonicity contributions to the molecular excited state internal conversion rates with finite temperature TD-DMRG

Abstract

In this work, we propose a new method to calculate molecular nonradiative electronic relaxation rates based on the numerically exact time-dependent density matrix renormalization group theory. This method could go beyond the existing frameworks under the harmonic approximation (HA) of the potential energy surface (PES) so that the anharmonic effect could be considered, which is of vital importance when the electronic energy gap is much larger than the vibrational frequency. We calculate the internal conversion (IC) rates in a two-mode model with Morse potential to investigate the validity of HA. We find that HA is unsatisfactory unless only the lowest several vibrational states of the lower electronic state are involved in the transition process when the adiabatic excitation energy is relatively low. As the excitation energy increases, HA first underestimates and then overestimates the IC rates when the excited state PES shifts toward the dissociative side of the ground state PES. On the contrary, HA slightly overestimates the IC rates when the excited state PES shifts toward the repulsive side. In both cases, a higher temperature enlarges the error of HA. As a real example to demonstrate the effectiveness and scalability of the method, we calculate the IC rates of azulene from S1 to S0 on the ab initio anharmonic PES approximated by the one-mode representation. The calculated IC rates of azulene under HA are consistent with the analytically exact results. The rates on the anharmonic PES are 30%–40% higher than the rates under HA.

Theoretical insights into the central “acceptor” bridge function on the whole visible light and near-infrared emission in tetraphenylpyrazine-based luminogens

“…Finally, it should be mentioned that although the method we employed has achieved satisfactory results in mechanism explanation and property prediction, quantitative modulation of the luminescent behaviors of organic materials is still challenging. 32,[47][48][49][50]…”

Structure–property relationship study of blue thermally activated delayed fluorescence molecules with different donor and position substitutions: theoretical perspective and molecular design

“…48 Both, the detailed methodology and simulation method of the above formalism can be found in the works of Peng, Shuai and us. 49–55 In addition, the frontier molecular orbitals, intramolecular interactions and natural transition orbit (NTO) analyses were performed following Multiwfn. 56…”

Matrix Product State Formulation of the MCTDH Theory in Local Mode Representations for Anharmonic Potentials

“…The density matrix renormalization group (DMRG) algorithm , is one of the promising methods to circumvent such exponential complexity, in which the exponentially growing parameters are decomposed to sequentially coupled small tensors called site functions. Time-dependent versions of the DMRG have been used for a wide variety of applications ranging from the spin dynamics to realistic quantum dynamics simulations of molecular systems. − In our recent study, we have proposed the matrix product state formulation (MPS-MCTDH) theory, in which not only the site functions but also the one-particle basis, namely site basis states, are allowed to vary with time under the variational principle, like as in the multiconfigurational time-dependent Hartree (MCTDH) theory. The time propagation of the one-particle basis is particularly important for simulating the quantum dynamics of realistic molecular systems in an ab initio manner, in which the potential energy surfaces should not be approximated by simple parabolas.…”