TY  - JOUR
A1  - Martinazzo, Rocco
A1  - Nest, Mathias
A1  - Saalfrank, Peter
A1  - Tantardini, Gian Franco
T1  - A local coherent-state approximation to system-bath quantum dynamics
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - A novel quantum method to deal with typical system-bath dynamical problems is introduced. Subsystem discrete variable representation and bath coherent-state sets are used to write down a multiconfigurational expansion of the wave function of the whole system. With the help of the Dirac-Frenkel variational principle, simple equations of motion-a kind of Schrodinger-Langevin equation for the subsystem coupled to (pseudo) classical equations for the bath-are derived. True dissipative dynamics at all times is obtained by coupling the bath to a secondary, classical Ohmic bath, which is modeled by adding a friction coefficient in the derived pseudoclassical bath equations. The resulting equations are then solved for a number of model problems, ranging from tunneling to vibrational relaxation dynamics. Comparison of the results with those of exact, multiconfiguration time-dependent Hartree calculations in systems with up to 80 bath oscillators shows that the proposed method can be very accurate and might be of help in studying realistic problems with very large baths. To this end, its linear scaling behavior with respect to the number of bath degrees of freedom is shown in practice with model calculations using tens of thousands of bath oscillators.
Y1  - 2006
U6  - https://doi.org/10.1063/1.2362821
SN  - 0021-9606
SN  - 1089-7690
VL  - 125
IS  - 19
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Bouakline, Foudhil
A1  - Lüder, Franziska
A1  - Martinazzo, Rocco
A1  - Saalfrank, Peter
T1  - Reduced and exact quantum dynamics of the vibrational relaxation of a molecular system interacting with a finite-dimensional bath
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - We investigate the vibrational relaxation of a Morse oscillator, nonlinearly coupled to a finite-dimensional bath of harmonic oscillators at zero temperature, using two different approaches: Reduced dynamics with the help of the Lindblad formalism of reduced density matrix theory in combination with Fermi's Golden Rule, and exact dynamics (within the chosen model). with the multiconfiguration time-dependent Hartree (MCTDH) method. Two different models have been constructed, the situation where the bath spectrum is exactly resonant with the anharmonic oscillator transition frequencies, and the case for which the subsystem is slightly off-resonant with the environment. At short times, reduced dynamics calculations describe the relaxation process qualitatively well but fail to reproduce recurrences observed with MCTDH for longer times. Lifetimes of all the vibrational levels of the Morse oscillator have been calculated, and both Lindblad and MCTDH. results show the same dependence of the lifetimes on the initial vibrational state quantum number. A prediction, which should be generic for adsorbate systems is a striking, sharp increase of lifetimes of the subsystem vibrational levels close to the dissociation This is contradictory with harmonic/linear extrapolation laws, which predict a monotonic decrease of the lifetime with initial vibrational quantum number.
Y1  - 2012
U6  - https://doi.org/10.1021/jp304466u
SN  - 1089-5639
VL  - 116
IS  - 46
SP  - 11118
EP  - 11127
PB  - American Chemical Society
CY  - Washington
ER  -