Propagative block diagonalization diabatization of DFT/MRCI electronic states

Abstract

We present a framework for the calculation of diabatic states using the combined density functional theory and multireference configuration interaction (DFT/MRCI) method. Due to restrictions present in the current formulation of the DFT/MRCI method (a lack of analytical derivative couplings and the inability to use non-canonical Kohn-Sham orbitals), most common diabatisation strategies are not applicable. We demonstrate, however, that diabatic wavefunctions and potentials can be calculated at the DFT/MRCI level of theory using a propagative variant of the block diagonalisation diabatisation method (P-BDD). The proposed procedure is validated via the calculation of diabatic potentials for LiH and the simulation of the vibronic spectrum of pyrazine. In both cases, the combination of the DFT/MRCI and P-BDD methods is found to correctly recover the non-adiabatic coupling effects of the problem.

Vacuum Ultraviolet Excited State Dynamics of the Smallest Ketone: Acetone

“…The quantum dynamics calculations were performed using the MCTDH method − in conjunction with a truncated quartic vibronic coupling Hamiltonian. − The diabatic potential was obtained by fitting a 1-mode fourth-order expansion to diabatic potentials and couplings computed at the combined density functional theory and multireference configuration interaction (DFT/MRCI) − level of theory using a propagative block diagonalization diabatization scheme. − In these calculations, the aug-cc-pVDZ basis was used. Absorption and photoelectron spectra were computed from the Fourier transforms of the wavepacket autocorrelation functions obtained following vertical excitation to the final states of interest.…”

Which form of the molecular Hamiltonian is the most suitable for simulating the nonadiabatic quantum dynamics at a conical intersection?

“…we denote the residual nonadiabatic vector couplings by F qd (Q) and residual nonadiabatic scalar couplings by G qd (Q). Different transformation matrices S(Q) are obtained by different quasidiabatization schemes, 64 which include the block-diagonalization of the reference Hamiltonian matrix, 43,[66][67][68] integration of the nonadiabatic couplings, 69-73 use of the molecular properties, [74][75][76][77][78][79][80] and construction of regularized quasidiabatic states. 42,45,81 We have chosen to quasidiabatize the molecular Hamiltonian with this regularized diabatization scheme because of its simplicity.…”

How important are the residual nonadiabatic couplings for an accurate simulation of nonadiabatic quantum dynamics in a quasidiabatic representation?

“…is obtained by any of the many quasidiabatization schemes, 20,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] but the magnitude of the residual nonadiabatic couplings depends on the quasidiabatization scheme. Following…”

“…Quasidiabatization of the molecular Hamiltonian by a coordinate-dependent unitary transformation [20][21][22] rectifies this singularity of the nonadiabatic couplings. The transformation matrix can be obtained by various quasidiabatization schemes, of which a few representative examples include the methods based on the integration of the nonadiabatic couplings [23][24][25][26][27] or on different molecular properties [28][29][30][31][32][33][34] and the block-diagonalization [35][36][37][38] or regularized diabatization [39][40][41] schemes. For more than one nuclear dimension, however, no quasidiabatization scheme leads to the strictly diabatic states, i.e., states in which the nonadiabatic couplings are eliminated completely, unless infinitely many electronic states are considered.…”