We investigate the molecular dynamics of pyrazine after excitation to the S2 electronic state by using the time-dependent discrete variable representation (TDDVR) method. The investigation has been carried out with a realistic 24-mode model Hamiltonian consisting of all the vibrational degrees of freedom of pyrazine molecule. First, we perform the simulation on a basic four-mode model, and then by including additional eight important modes and finally, by introducing 20 bath modes on the basic model. This sequential inclusion of bath modes demonstrates the effect of weak modes on the subsystem, where the calculations of energy and population transfer from basic model to the bath quantify the same effect. The spectral profile obtained by using TDDVR approach shows reasonably good agreement with the results calculated by quantum mechanical approach. It appears that the TDDVR approach for those large systems where quantum mechanical description is needed in a restricted region is a good compromise between accuracy and speed.

We have used the time-dependent discrete variable representation (TDDVR) method to simulate the photoabsorption spectrum of pyrazine. The time-dependent molecular dynamics of pyrazine after excitation to the S2 electronic state is considered as a benchmark to investigate the S2 absorption spectrum. We have carried out the dynamics on a basic four-mode model of pyrazine with the inclusion of five major modes as well as the rest of the vibrational modes as bath modes. Investigations reveal the effect of bath modes such as energy and population transfer from the subsystem to the bath. Calculated results demonstrate excellent agreement with traditional quantum-mechanical findings during the entire propagation and converge to the exact quantum results when enough gridpoints are used. It appears that TDDVR, as a numerical quantum dynamics methodology, is a good compromise between accuracy and speed.

ABSTRACT:The time-dependent discrete variable representation (TDDVR) of a wave function with grid points defined by the Hermite part of the Gauss-Hermite (G-H) basis set introduces quantum corrections to classical mechanics. The grid points in this method follow classical trajectory and the approach converges to the exact quantum formulation with sufficient trajectories (TDDVR points) but just with a single grid point; only classical mechanics performs the dynamics. This newly formulated approach (developed for handling time-dependent molecular quantum dynamics) has been explored to calculate vibrational transitions in the inelastic scattering processes. Traditional quantum mechanical results exhibit an excellent agreement with TDDVR profiles during the entire propagation when enough grid points are included in the quantum-classical dynamics.

ABSTRACT:In this article, we apply a novel time-dependent discrete variable representation (TDDVR) method proposed by Barkakaty and Adhikari to investigate tunneling through an Eckart barrier. This semi-classical method is theoretically rigorous and straightforward to implement. Among the TDDVR formulations, this report presents the first derivation of a rigorous form of quantum force (QF) for the present perspective. The validity of this semi-classical approach is demanded based on the excellent agreement of the tunneling probability with the corresponding quantum results.

We demonstrate the workability of a TDDVR based [J. Chem. Phys. 118, 5302 (2003)], novel quantum-classical approach, for simulating scattering processes on a quasi-Jahn-Teller model [J. Chem. Phys. 105, 9141 (1996)] surface. The formulation introduces a set of DVR grid points defined by the Hermite part of the basis set in each dimension and allows the movement of grid points around the central trajectory. With enough trajectories (grid points), the method converges to the exact quantum formulation whereas with only one grid point, we recover the conventional molecular dynamics approach. The time-dependent Schrodinger equation and classical equations of motion are solved self-consistently and electronic transitions are allowed anywhere in the configuration space among any number of coupled states. Quantum-classical calculations are performed on diabatic surfaces (two and three) to reveal the effects of symmetry on inelastic and reactive state-to-state transition probabilities, along with calculations on an adiabatic surface with ordinary Born-Oppenheimer approximation. Excellent agreement between TDDVR and DVR results is obtained in both the representations.

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A hybrid heteronanostructure of α-MnO 2 /Mn 3 O 4 /CeO 2 with the atomic-level coupled nanointerface entrenched in Vulcan carbon is reported and explored for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). CeO 2 plays an essential role in increasing the surface Mn 2+/3+/4+ in α-MnO 2 /Mn 3 O 4 /CeO 2 /C for ORR/OER processes. It shows enhanced bifunctional activity, superior to that of the benchmark 20 wt % Pt/C and Pd/C catalysts. It displays an ORR onset potential of −0.13 V (vs Ag/AgCl), limiting current density of −6.63 mA cm −2 (at 1600 rpm), mass-specific current of 47.6 mA mg MO −1 with a lower Tafel slope (921.9 mV dec −1 ), and an inclusive 4-e transfer involved in ORR. The OER onset potential and current density are 0.58 V (vs Ag/AgCl) and 8.45 mA cm −2 (at 0.8 V). The unique hybrid structure with oxide−oxide interface in α-MnO 2 / Mn 3 O 4 /CeO 2 is correlated to explain the mechanistic pathway. Multistate Mn(II/III/IV) and Ce(III/IV) synergistically influence in tendering superior activity with enhanced stability.