Accurate quantum calculations of thermal rate constants employing MCTDH: H2+OH→H+H2O and D2+OH→D+DOH

Abstract

Potential energy surface for a seven-atom reaction. Thermal rate constants and kinetic isotope effects for CH 4 +OH An improved approach for the direct calculation of thermal rate constants, employing the multi-configurational time-dependent Hartree ͑MCTDH͒ approach and the flux-flux correlation function, is presented. In this approach, the thermal flux operator is diagonalized and its eigenstates are propagated. The cumulative reaction probability is obtained for all energies simultaneously by a simple Fourier transform of the matrix elements between the propagated flux eigenstates. Calculations for the H 2 ϩOH→HϩH 2 O reaction, which include all six internal degrees of freedom accurately, demonstrate the accuracy and efficiency of the approach. Previous results for the rate constant are reproduced ͑for temperatures between 300 K and 600 K͒ and extended towards lower temperatures ͑200 K to 300 K͒. Also, thermal rate constants of the D 2 ϩOH→DϩDOH reaction have been computed. All six internal degrees of freedom are included accurately in this calculation. The kinetic isotope effect is obtained and compared to experiment.

State-to-state reaction probabilities within the quantum transition state framework

“…The quantum transition state concept facilitates an efficient scheme for calculating cumulative reaction probability (CRP), thermal rate constants, 27,28,[30][31][32][33][34][35][36][37][38][39]41 and initial stateselected reaction probabilities. 29,32,40 Starting from flux correlation functions [45][46][47] the CRP can be written as…”

“…Accurate full-dimensional quantum dynamics calculations for six atom reactions have up to now only been presented for cumulative reaction probabilities and thermal rate constants [14][15][16][17][18][19][20][21][22][23] or initial state-selected reaction probabilities 24,25 and studied the H + CH 4 → H 2 + CH 3 , [14][15][16][17][18][19][22][23][24][25] [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] and propagated wave packets representing vibrational states of the activated complex which have been a) Electronic mail: rwelsch@uni-bielefeld.de. b) Electronic mail: uwe.manthe@uni-bielefeld.…”

An extension of the grid empowered molecular simulator to quantum reactive scattering

“…The basic outcome of these two programs is the scattering S matrix from which reaction probabilities, cross sections, and rate coefficients can be derived. More detailed More demanding has been the work needed to extend GEMS to include the MCTDH-FC code [9,10] (see the leftmost box of the dynamics block of Figure 1). In the MCTDH method, the nuclear TD Schrödinger equation is solved for multidimensional dynamical systems consisting of distinguishable particles using the Dirac Frenkel variational method.…”

“…In the MCTDH method, the nuclear TD Schrödinger equation is solved for multidimensional dynamical systems consisting of distinguishable particles using the Dirac Frenkel variational method. [10,13] The associated configurations are formed as direct products of one variable TD basis functions, called single-particle functions (SPFs). This approach leads to a set of coupled equations of motion for the expansion coefficients and for the set of functions used to build the Hartree product configurations.…”

“…[9,10] The article is structured as follows. In An overview of theoretical and computational approaches to quantum reactive problems section, an overview on the theoretical and computational machinery developed in COST D37 to the end of extending GEMS to quantum methods is given.…”