Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

Development of a machine learning potential for graphene

Abstract: We present an accurate interatomic potential for graphene, constructed using the Gaussian approximation potential (GAP) machine learning methodology. This GAP model obtains a faithful representation of a density functional theory (DFT) potential energy surface, facilitating highly accurate (approaching the accuracy of ab initio methods) molecular dynamics simulations. This is achieved at a computational cost which is orders of magnitude lower than that of comparable calculations which directly invoke electronic structure methods. We evaluate the accuracy of our machine learning model alongside that of a number of popular empirical and bond-order potentials, using both experimental and ab initio data as references. We find that whilst significant discrepancies exist between the empirical interatomic potentials and the reference data—and amongst the empirical potentials themselves—the machine learning model introduced here provides exemplary performance in all of the tested areas. The calculated properties include: graphene phonon dispersion curves at 0 K (which we predict with sub-meV accuracy), phonon spectra at finite temperature, in-plane thermal expansion up to 2500 K as compared to NPT ab initio molecular dynamics simulations and a comparison of the thermally induced dispersion of graphene Raman bands to experimental observations. We have made our potential freely available online at [http://www.libatoms.org].

Extended Born-Oppenheimer molecular dynamics

Abstract: A Lagrangian generalization of time-reversible Born-Oppenheimer molecular dynamics Niklasson et al. [Phys. Rev. Lett. 97, 123001 (2006)] is proposed. The formulation enables the application of higher-order symplectic or geometric integration schemes that are stable and energy conserving even under incomplete self-consistency convergence. It is demonstrated how the accuracy is improved by over an order of magnitude compared to previous formulations at the same level of computational cost. The proposed Lagrangian includes extended electronic degrees of freedom as auxiliary dynamical variables in addition to the nuclear coordinates and momenta. While the nuclear degrees of freedom propagate on the Born-Oppenheimer potential energy surface, the extended auxiliary electronic degrees of freedom evolve as a harmonic oscillator centered around the adiabatic propagation of the self-consistent ground state.

The spin-conserved reaction CH+N2→H+NCN: A major pathway to prompt no studied by quantum/statistical theory calculations and kinetic modeling of rate constant

Abstract: A new spin-conserved path for the CH(2H)+N2 reaction at temperatures relevant to prompt NO formation has been theoretically investigated by means of ab initio MO calculations at the G2M level of theory. The result of the calculation reveals that the CH(2H)+N2 reaction takes place primarily via the ground electronic doublet potential energy surface, producing H+NCN instead of the commonly assumed, spin-forbidden HCN+N(4S) products. The overall rate constant for NCN production has been computed by a multichamel canonical variational Rice-Ramsperger-Kassel-Marcus theory calculation for the temperature range 1500–4000 K at 0.5–2 atm pressure: k3=2.22×107 T1.48 exp (−11760/T) cm3/(mol·s). The theoretically predicted rate constant was found to be in good agreement with high-temperature shock tube data kinetically modeled with the new mechahism that includes NCN reactions. In addition, k, was also found to be consistent with the apparent rate constants previously modeled for prompt NO formation in several flamer studies.

Photodissociation dynamics of H2O and D2O in the first absorption band: A complete abinitio treatment

Abstract: We report a detailed theortical study of the photodissociation of H2O and D2O in the first absorption band (λ∼165 nm). The calculations are three dimensional and purely quantum mechanical. They include an ab initio potential energy surface for the A state and a calculated SCF dipole moment function for the X→A transition. The dynamical calculations are performed within the infinite‐order‐sudden approximation for the rotational degree of freedom of OH and the LHL approximation for the masses. The resulting vibrational–translational motion is then treated exactly in two dimensions using hyperspherical coordinates. This study does not include any adjustable parameters. The thermally averaged total absorption spectra for H2O and D2O agree perfectly with the experimental spectra. Even finer details such as the progression of ‘‘vibrational’’ structures are well reproduced. They are not induced by any selective absorption but can be explained on the basis of the A state potential energy surface and details o...

Super-Reduced Polyoxometalates: Excellent Molecular Cluster Battery Components and Semipermeable Molecular Capacitors

Abstract: Theoretical investigations are presented on the molecular and electronic structure changes that occur as α-Keggin-type polyoxometalate (POM3–) clusters [PM12O40]3– (M = Mo, W) are converted toward their super-reduced POM27– state during the discharging process in lithium-based molecular cluster batteries. Density functional theory was employed in geometry optimization, and first-principles molecular dynamics simulations were used to explore local minima on the potential energy surface of neutral POM clusters adorned with randomly placed Li atoms as electron donors around the cluster surface. On the basis of structural, electron density, and molecular orbital studies, we present evidence that the super-reduction is accompanied by metal–metal bond formation, beginning from the 12th to 14th excess electron transferred to the cluster. Afterward, the number of metal–metal bonds increases nearly linearly with the number of additionally transferred excess electrons. In α-Keggin-type POMs, metal triangles are a p...