Molecular dynamics approach to vibrational energy relaxation: Quantum-classical versus purely classical nonequilibrium simulations

The Ehrenfest method with quantum corrections is used to describe the vibrational relaxation of the bend fundamental in liquid water. All the vibrational degrees of freedom of the water molecules are described using quantum mechanics, while the remaining translational and rotational degrees of freedom are described classically. The relaxation time obtained compares well with experiment and with relaxation times calculated using other theoretical approximations. The presence of resonant intermolecular vibrational energy (VV) transfer is established with a maximum percentage of excited molecules, different from the initial one, of 9.2%. It is found through an effective kinetic fit that two VV transfers occur before relaxation of water to the vibrational ground state.

Section: A the Ehrenfest Methods With Quantum Correctionsmentioning

confidence: 99%

Hybrid quantum/classical simulation of the vibrational relaxation of the bend fundamental in liquid water

Bastida

Zúñiga

Requena

et al. 2009

“…[11][12][13] In terms of accuracy, our analytical treatment cannot compete, of course, with quantum scattering calculations. For the N 2 -He example, our analytical formulas describe the temperature dependence of k 10 over eight orders of magnitude, while the absolute value of k 10 is recovered by fitting a single parameter only, the preexponential factor in the expression for the rate.…”

Section: Summarizing Remarksmentioning

confidence: 99%

“…5 If within this approach one takes advantage of two important features of vibrationally inelastic collisions, namely the weak coupling of the vibrational mode to the heat-bath modes for transitions between low-lying vibrational states and the quasiclassical character of the heat-bath modes, one can use the general formalism of the linear response theory. [8][9][10][11][12][13][14][15] We also have recently discussed this problem 16 and suggested the way to restore the detailed balance relation by using the semiclassical ͑SC͒ approximation as described in the Landau and Lifshitz's textbook 17 where it is called the quasiclassical approximation. In short, when the quantum of vibrational energy ⌬E is released into the heat bath of temperature T under the condition that the former is comparable with or larger than kT, it produces a strong local perturbation in the bath modes irrespective of the coupling strength between the vibrational and the bath degrees of freedom.…”

Section: Introductionmentioning

confidence: 99%

Semiclassical extension of the Landau-Teller theory of collisional energy transfer

Dashevskaya

Nikitin

Troe

2006

Self Cite

A semiclassical version of the quantum coupled-states approximation for the vibrational relaxation of diatomic molecules in collisions with monatomic bath gases is presented. It is based on the effective mass approximation and a recovery of the semiclassical Landau exponent from the classical Landau-Teller collision time. For an interaction with small anisotropy, the Landau exponent includes first order corrections with respect to the orientational dependence of the collision time and the effective mass. The relaxation N(2)(v=1)-->N(2)(v=0) in He is discussed as an example. Employing the available vibrationally elastic potential, the semiclassical approach describes the temperature dependence of the rate constant k(10)(T) over seven orders of magnitude across the temperature range of 70-3000 K in agreement with experimental data and quantum coupled-states calculations. For this system, the hierarchy of corrections to the Landau-Teller conventional treatment in the order of importance is the following: quantum effects in the energy release, dynamical contributions of the rotation of N(2) to the vibrational transition, and deviations of the interaction potential from a purely repulsive form. The described treatment provides significant simplifications over complete coupled-states calculations such that applications to more complex situations appear promising.

“…1͑a͒. Thus, the role of the slipped initial conditions is similar to those in the corresponding quantum-classical treatment, 26 where they remove the breakdown of the positivity of the RDM within the applicability limits of the approach. In the second case ͑b͒ the initial values for auxiliary functions are naturally zero, but at the same time the kinetics does not exhibit unphysical features, see Fig.…”

Section: ͑33͒mentioning

confidence: 83%

“…26 on the basis of a simple four-level system. The replacement of quantum operators by the phase space coordinates in the framework of partial Wigner transforms of the quantum Liouville-von Neumann equation also leads to the replacement of true cross coherences, which drive the energy flow between the subsystems, by direct coherences inside quantum subsystem, as it was well explained in Ref.…”

Section: Introductionmentioning

confidence: 99%

Non-Markovian theory of open systems in classical limit

Neufeld

2004

Self Cite

A fully classical limit of the recently published quantum-classical approximation [A. A. Neufeld, J. Chem. Phys. 119, 2488 (2003)] is obtained and analyzed. The resulting kinetic equations are capable of describing the evolution of an open system on the entire time axis, including the short-time non-Markovian stage, and are valid beyond linear response regime. We have shown, that proceeding to the classical mechanics limit we restrict the class of allowed correlations between an open system and a canonical bath, so that the initial conditions and the relaxation operator has to be appropriately modified (projected). Disregard of the projection may lead to unphysical behavior, since mechanism of the decay of some correlations is essentially of quantum-mechanical nature, and is not correctly described by classical mechanics. The projection (quantum correction to the kinetics) is particularly important for the non-Markovian regime of relaxation towards canonical equilibrium. The conformity of the developed method to the conventional approaches is demonstrated using a model of Brownian motion (heavy particle in the bath of light ones), for which the obtained non-Markovian equations are reduced to the standard Fokker-Planck equation in phase space.