Using Hessian update formulae to construct modified Shepard interpolated potential energy surfaces: Application to vibrating surface atoms

Modified Shepard interpolation based on second order Taylor series expansions has proven to be a flexible tool for constructing potential energy surfaces in a range of situations. Extending this to gas-surface dynamics where surface atoms are allowed to move represents a substantial increase in the dimensionality of the problem, reflected in a dramatic increase in the computational cost of the required Hessian (matrix of second derivatives) evaluations. This work demonstrates that using approximate Hessians derived from well known Hessian update formulae and a single accurate Hessian can provide an effective way to avoid this expensive accurate Hessian determination.This work was supported by the NCI National Facility at the ANU

Basis expansion leaping: A new method to solve the time-dependent Schrödinger equation for molecular quantum dynamics

A wide variety of molecular systems that have recently come into the reach of experimental and theoretical investigation is dominated by quantum phenomena. However, even state of the art quantum propagation techniques are either unsuitable for general ap

Fast, scalable master equation solution algorithms. III. Direct time propagation accelerated by a diffusion approximation preconditioned iterative solver

In this paper we propose a novel fast and linearly scalable method for solving master equations arising in the context of gas-phase reactive systems, based on an existent stiff ordinary differential equation integrator. The required solution of a linear system involving the Jacobian matrix is achieved using the GMRES iteration preconditioned using the diffusion approximation to the master equation. In this way we avoid the cubic scaling of traditional master equationsolution methods and maintain the low temperature robustness of numerical integration. The method is tested using a master equation modelling the formation of propargyl from the reaction of singlet methylene with acetylene, proceeding through long lived isomerizing intermediates

Interpolating DFT Data for 15D Modeling of Methane Dissociation on an fcc Metal

Detailed simulation of reactions occurring on and with the surfaces of crystalline materials usually require a continuous representation of the potential energy surface that describes the adsorbate–surface interaction. Only a few techniques are available to describe interactions with polyatomic adsorbates that respect all of the symmetries of the interactions. The modified Shepard interpolation has recently been reformulated to ensure symmetries are rigorously imposed. In this work, the modified Shepard interpolation is used to construct a 15D potential energy surface for the reaction of methane with the {100} surface of a face-centered cubic metal, in the Born--Oppenheimer static surface (BOSS) approximation. The energy of the system is calculated using density functional theory (DFT), and the geometries around which the potential is expanded are selected by quasi-classical trajectory calculations. The energy of the resulting continuous potential energy surface exactly matched the DFT energy at these points; there is no fitting error. It is demonstrated that the classical reaction probability converges with a reasonable number of interpolation points for this 15D system.This work was supported by the NCI National Facility at the ANU. The author acknowledges the support of the Australian Research Council through a Future Fellowship (FT100100824) and Discovery Project grant (DP160100059)

First crystal structure studies of CaAlH5

A new member of the aluminum hydride family, CaAlH5, is formed during the decomposition of Ca(AlH4)2. The crystal structure of this new compound was calculated by density functional theory band-structure calculations and confirmed by X-ray powder diffraction analysis. The structure crystallizes in space group P21/n (No. 14), with a = 8.3797(9) Å, b = 6.9293(8) Å, c = 9.8138(11) Å, β = 93.78(1)°, and Z = 8

Modified Shepard interpolation of gas-surface potential energy surfaces with strict plane group symmetry and translational periodicity

A new formulation of modified Shepard interpolation of potential energy surface data for gas-surface reactions has been developed. The approach has been formulated for monoatomic or polyatomic adsorbates interacting with crystalline solid surfaces of any plane group symmetry. The interpolation obeys the two dimensional translational periodicity and plane group symmetry of the solid surface by construction. The interpolation remains continuous and smooth everywhere. The interpolation developed here is suitable for constructing potential energy surfaces by sampling classical trajectories using the Grow procedure. A model function has been used to demonstrate the method, showing the convergence of the classical gas-surface reaction probability

The dynamics of the H₂+CO⁺ reaction on an interpolated potential energy surface

A potential energy surface that describes the title reaction has been constructed by interpolation of ab initio data. Classical trajectory studies on this surface show that the total reaction rate is close to that predicted by a Langevin model, although the mechanism is more complicated than simple ion-molecule capture. Only the HCO⁺ + H product is observed classically. An estimate of the magnitude of rotational inelastic scattering is also reported.financial support from the Ministry of Science, Research and Technology of Iran, and from Shiraz University

Density functional theory modeling of critical properties of perovskite oxides for water splitting applications

Water splitting (WS) driven by solar energy is considered as a promising strategy to produce renewable hydrogen from water with minimal environmental impact. Realization of large-scale hydrogen production by this approach requires cost-effective, efficient and stable materials to drive the WS reaction. Perovskite oxides have recently attracted widespread attention in WS applications due to their unique structural features, such as compositional and structural flexibility allowing them to achieve desired sunlight absorption capability, precise control of electrocatalytic and redox activity to drive the chemical reaction, tuneable bandgaps and band edges, and earth-abundance. However, perovskite oxides contain a large family of metal oxides and experimental exploration of novel perovskites without a priori knowledge of their properties could be costly and time-consuming. First-principles approaches such as density functional theory (DFT) are a useful and cost-effective alternative towards this end. In this review, DFT-based calculations for accurate prediction of the critical properties of ABO3 perovskite oxides relevant to WS processes are surveyed. Structural, electronic, optical, surface, and thermal properties are grouped according to their relevance to photocatalytic (PC), electrochemical (EC), photo-electrochemical (PEC), and solar thermal water splitting (STWS) processes. The challenges associated with the choice of exchange-correlation (XC) functional in DFT methods for precise prediction of these properties are discussed and specific XC functionals have been recommended where experimental comparisons are possible

Fast, scalable master equation solution algorithms. IV. Lanczos iteration with diffusion approximation preconditioned iterative inversion

In this paper we propose a second linearly scalable method for solving large master equations arising in the context of gas-phase reactive systems. The new method is based on the well-known shift-invert Lanczos iteration using the GMRES iteration preconditioned using the diffusion approximation to the master equation to provide the inverse of the master equation matrix. In this way we avoid the cubic scaling of traditional master equation solution methods while maintaining the speed of a partial spectral decomposition. The method is tested using a master equation modeling the formation of propargyl from the reaction of singlet methylene with acetylene, proceeding through long-lived isomerizing intermediates. (C) 2003 American Institute of Physics