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.

A molecular dynamics simulation study with a combined quantum mechanical and molecular mechanical potential energy function: Solvation effects on the conformational equilibrium of dimethoxyethane

Abstract: Solvent effects on the conformational equilibria of dimethoxyethane (DME, CH3–O–CH2–CH2–O–CH3) have been studied using molecular dynamics simulation with a combined molecular mechanical and semiempirical quantum mechanical potential energy function. The potential of mean force around the central O–C–C–O dihedral angle of DME in water was determined using umbrella sampling, with the DME molecule treated by the modified intermediate neglect of diatomic differential overlap (MNDO) method and water molecules described using the extended simple point charge model. This potential of mean force shows the same bias as the gas phase potential energy surface calculated by MNDO: the heights of the barriers are underestimated and the stability of the gauche conformation with respect to the trans conformation is overestimated. However, the calculated stabilization of the gauche state by solvation is in good agreement with experimental results, suggesting a quite reasonable description of this system by the combined po...

Potential energy surface for cyclotrimethylene trinitramine dimer from symmetry-adapted perturbation theory

Abstract: We present a potential energy surface (PES) for the cyclotrimethylene trinitramine (RDX) dimer obtained using symmetry-adapted perturbation theory based on the Kohn–Sham density functional theory (DFT) description of the monomers [SAPT(DFT)]. More than a thousand dimer configurations were computed using an augmented double-zeta-quality basis set supplemented by bond functions. The ab initio interaction energies were used to obtain a six-dimensional analytic fit of the interaction PES. The geometries and energies of the minima on the PES have been found from the fit. The decomposition of the PES into physical components provided by the SAPT(DFT) method has been analyzed. The PES was then used in molecular dynamics simulations of the RDX crystal. The predicted crystal density is in an excellent agreement with experiment.

Interaction potentials and rovibrational spectroscopy of HeN-OCS complexes

Abstract: We present a new vibrationally averaged He-OCS potential energy surface that is obtained from a combination of Moller-Plesset perturbation theory for the helium-molecule interaction and coupled cluster theory for the intramolecular vibrational potential. Employing this potential in quantum Monte Carlo calculations for He(N)-OCS complexes shows a blueshift of the OCS vibration for small N that is followed by a transition to a redshift for larger N. The size dependence of the vibrational shift is in good agreement with recent experimental measurements. We then make a comparative study of the effective rotational spectroscopic constants B(eff) and D(eff) calculated for small N values with this vibrationally averaged potential, with the corresponding values obtained from three previous He-OCS potentials. We find that the vibrationally averaged potential provides the most accurate description of the spectroscopic constants over the size range N=1-8 for which experimental data are available. We rationalize this improved description in terms of the detailed differences in the secondary minimum and saddle point regions of the underlying He-OCS interaction potential, in addition to the behavior at the lowest potential minimum. This analysis indicates that the spectroscopy of complexes with N>1 provides valuable information on the shape of the potential energy surface in regions that are not accessed by the N=1 He-OCS complex, but that are important for understanding the molecular spectroscopy in larger complexes and in droplets.

Quantum rate constants for the H2+OH reaction with the centrifugal sudden approximation

Abstract: The cumulative reaction probability (CRP) has been calculated for the H2+OH↔H2O+H in its full dimensionality by using the centrifugal sudden (CS) approximation for J>0. The Boltzmann average of the CRP provides the most accurate thermal rate constant to date for the title reaction on the Walch, Dunning, Schatz, Elgersma (WDSE) potential energy surface (PES). It is found that the theoretical rate is larger than the experimental value in the low temperature region (a factor of ∼1.8 at 300 K), and smaller than the experimental value for temperatures higher than 500 K, indicating that a more accurate PES is needed to provide a quantitative description of the title reaction. We also demonstrate that the “J-shifting” approximation in which we calculate N(J>K,K) from N(J=K,K) by an energy shift works very well for this reaction. However, the “J- and K-shifting” approximation [calculating N(J,K) from N(J=0,K=0)] overestimates the rate for this reaction by about 60% for all the temperatures investigated. It is als...