38,025 research outputs found
Molecular potential energy surfaces by interpolation: Strategies for faster convergence
A method for interpolating molecular potential energy surfaces introduced [Ischtwan and Collins, J. Chem. Phys. 100, 8080 (1994)] and developed as an iterative scheme has been improved by different criteria for the selection of the data points. Refinements in the selection procedure are based on the variance of the interpolation and the direct exploration of the interpolation error, and produce more accurate surfaces than the previously established scheme for the same number of data points
Ab initio potential energy surface and quantum dynamics for the H + CH₄ → H₂+ CH₃ reaction
A new full-dimensional potential energy surface for the title reaction has been constructed using the modified Shepard interpolation scheme. Energies and derivatives were calculated using the UCCSD(T) method with aug-cc-pVTZ and 6-311++G(3df,2pd) basis sets, respectively. A total number of 30,000 data points were selected from a huge number of molecular configurations sampled by trajectory method. Quantum dynamical calculations showed that the potential energy surface is well converged for the number of data points for collision energy up to 2.5 eV. Total reaction probabilities and integral cross sections were calculated on the present surface, as well as on the ZBB3 and EG-2008 surfaces for the title reaction. Satisfactory agreements were achieved between the present and the ZBB3 potential energy surfaces, indicating we are approaching the final stage to obtain a global potential energy surface of quantitative accuracy for this benchmark polyatomic system. Our calculations also showed that the EG-2008 surface is less accurate than the present and ZBB3 surfaces, particularly in high energy region.This work was mainly supported by the National Natural
Science Foundation of China (Grant Nos. 20833007 and
90921014), and the Chinese Academy of Sciences
Molecular potential energy surfaces constructed from interpolation of systematic fragment surfaces
A systematic method for approximating the ab initio electronic energy of molecules from the energies of molecular fragments has previously been presented. Here it is shown that this approach provides a feasible, systematic method for constructing a global molecular potential energy surface (PES) for reactions of a moderate-sized molecule from the corresponding surfaces for small molecular fragments. The method is demonstrated by construction of PESs for the reactions of a hydrogen atom with propane and n-pentane
Non-adiabatic effects during the dissociative adsorption of O2 at Ag(111)? A first-principles divide and conquer study
We study the gas-surface dynamics of O2 at Ag(111) with the particular
objective to unravel whether electronic non-adiabatic effects are contributing
to the experimentally established inertness of the surface with respect to
oxygen uptake. We employ a first-principles divide and conquer approach based
on an extensive density-functional theory mapping of the adiabatic potential
energy surface (PES) along the six O2 molecular degrees of freedom. Neural
networks are subsequently used to interpolate this grid data to a continuous
representation. The low computational cost with which forces are available from
this PES representation allows then for a sufficiently large number of
molecular dynamics trajectories to quantitatively determine the very low
initial dissociative sticking coefficient at this surface. Already these
adiabatic calculations yield dissociation probabilities close to the scattered
experimental data. Our analysis shows that this low reactivity is governed by
large energy barriers in excess of 1.1 eV very close to the surface.
Unfortunately, these adiabatic PES characteristics render the dissociative
sticking a rather insensitive quantity with respect to a potential spin or
charge non-adiabaticity in the O2-Ag(111) interaction. We correspondingly
attribute the remaining deviations between the computed and measured
dissociation probabilities primarily to unresolved experimental issues with
respect to surface imperfections.Comment: 18 pages including 6 figure
Interpolation for molecular dynamics simulations: from ions in gas phase to proteins in solution
The interpolation technique has shown many promises for simulating chemical dynamics with quantum chemical accuracy at molecular mechanics speed. This is achieved by constructing analytic potential energy surfaces with quantum chemical information at multiple conformational points, without assuming any functional form for the potentials. Here, we briefly review the course the method was developed over the past few decades, with a special focus on the activities in Korea. We also describe its strengths and weaknesses toward describing condensed phase chemical dynamics with the present implementations. Perspectives for future developments toward increasing applicability are discussed as concluding remarks. (c) 2015 Wiley Periodicals, Inc.1122Ysciescopu
Electron-hole pairs during the adsorption dynamics of O2 on Pd(100) - Exciting or not?
During the exothermic adsorption of molecules at solid surfaces dissipation
of the released energy occurs via the excitation of electronic and phononic
degrees of freedom. For metallic substrates the role of the nonadiabatic
electronic excitation channel has been controversially discussed, as the
absence of a band gap could favour an easy coupling to a manifold of
electronhole pairs of arbitrarily low energies. We analyse this situation for
the highly exothermic showcase system of molecular oxygen dissociating at
Pd(100), using time-dependent perturbation theory applied to first-principles
electronic-structure calculations. For a range of different trajectories of
impinging O2 molecules we compute largely varying electron-hole pair spectra,
which underlines the necessity to consider the high-dimensionality of the
surface dynamical process when assessing the total energy loss into this
dissipation channel. Despite the high Pd density of states at the Fermi level,
the concomitant non-adiabatic energy losses nevertheless never exceed about 5%
of the available chemisorption energy. While this supports an electronically
adiabatic description of the predominant heat dissipation into the phononic
system, we critically discuss the non-adiabatic excitations in the context of
the O2 spin transition during the dissociation process.Comment: 20 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.html [added two references, changed
V_{fsa} to V_{6D}, modified a few formulations in interpretation of spin
asymmetry of eh-spectra, added missing equals sign in Eg.(2.10)
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