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.

Accurate spectroscopic models for methane polyads derived from a potential energy surface using high-order contact transformations.

Abstract: A new spectroscopic model is developed for theoretical predictions of vibration-rotation line positions and line intensities of the methane molecule. Resonance coupling parameters of the effective polyad Hamiltionians were obtained via high-order contact transformations (CT) from ab initio potential energy surface. This allows converging vibrational and rotational levels to the accuracy of best variational calculations. Average discrepancy with centers of 100 reliably assigned experimental bands up to the triacontad range was 0.74 cm(-1) and 0.001 cm(-1) for GS rotational levels up to J = 17 in direct CT calculations without adjustable parameters. A subsequent "fine tuning" of the diagonal parameters allows achieving experimental accuracy for about 5600 Dyad and Pentad line positions, whereas all resonance coupling parameters were held fixed to ab initio values. Dipole transition moment parameters were determined from selected ab initio line strengths previously computed from a dipole moment surface by variational method. New polyad model allows generating a spectral line list for the Dyad and Pentad bands with the accuracy ~10(-3) cm(-1) for line positions combined with ab initio predictions for line intensities. The overall integrated intensity agreement with Hitran-2008 empirical database is of 4.4% for the Dyad and of 1.8% for the Pentad range.

The infrared spectrum of the O⋯H⋯O fragment of H5O2+: Ab initio classical molecular dynamics and quantum 4D model calculations

Abstract: The gas phase IR spectrum of the O⋯H⋯O fragment of H5O2+ and its deuterated analogue are calculated using ab initio classical molecular dynamics based on a MP2 potential energy surface. The assignment of the bands is made in terms of the quantum four-dimensional model calculations of anharmonic frequencies and intensities. Comparing low and high kinetic temperature simulations the importance of anharmonicities of the potential energy surface for understanding the vibrational band structure is highlighted. It is shown that any reasonable simulation of IR spectra of systems with very strong hydrogen bonds has to account for the dipole moment function beyond the linear approximation.

Ab initio potential energy and dipole moment surfaces of (H2O)2.

Abstract: A full-dimensional ab initio potential energy surface (PES) and dipole moment surface (DMS) are reported for the water dimer, (H2O)2. The CCSD(T)-PES is a very precise fit to 19 805 ab initio energies obtained with the coupled-cluster (CCSD(T)) method, using an aug-cc-pVTZ basis. The standard counterpoise correction was applied to approximately eliminate basis set superposition errors. The fit is based on an approach that incorporates the permutational symmetry of identical atoms [Huang, X.; Braams, B.; Bowman, J. M. J. Chem. Phys. 2005, 122, 044308]. The DMS is a fit to the dipole moment obtained with Moller−Plesset (MP2) theory, using an aug-cc-pVTZ basis. The PES has an RMS fitting error of 31 cm-1 for energies below 20 000 cm-1, relative to the global minimum. This surface can describe various internal floppy motions, including various monomer inversions, and isomerization pathways. Ten characteristic stationary points have been located on the surface, four of which are transition structures and the r...

QM/MM Car-Parrinello molecular dynamics study of the solvent effects on the ground state and on the first excited singlet state of acetone in water

Abstract: The authors present a hybrid Car-Parrinello quantum mech./mol. mech. (QM/MM) approach that is capable of treating the dynamics of mol. systems in electronically excited states in complex environments. The potential energy surface in the excited state is described either within the restricted open-shell Kohn-Sham (ROKS) formalism or within time-dependent d. functional theory (TDDFT). As a test case, the authors apply this technique to the study of the solvent effects on the ground state and on the first excited singlet state of acetone in water. Results demonstrate that for this system a purely classical description of the solvent is sufficient, since inclusion of the first solvent shell of 12 water mols. into the quantum system does not show a significant effect on this transition. The excited-state energies calcd. with ROKS are red shifted by a const. value compared to the TDDFT results, while the relative variations of the excitation energy for different configurations are in very good agreement. The exptl. obsd. blue shift of the excitation energy in going from gas phase to condensed phase is well reproduced. Excited-state dynamics carried out with ROKS yield the relaxation of the solute and the rearrangement of the solvent structure on a picosecond timescale. The calcd. Stokes shift is in reasonable agreement with exptl. data. [on SciFinder (R)]

Coherent structural dynamics of a prototypical charge-density-wave-to-metal transition.

Abstract: Using femtosecond time-resolved x-ray diffraction, we directly monitor the coherent lattice dynamics through an ultrafast charge-density-wave-to-metal transition in the prototypical Peierls system K(0.3)MoO(3) over a wide range of relevant excitation fluences. While in the low fluence regime we directly follow the structural dynamics associated with the collective amplitude mode; for fluences above the melting threshold of the electronic density modulation we observe a transient recovery of the periodic lattice distortion. We can describe these structural dynamics as a motion along the coordinate of the Peierls distortion triggered by the prompt collapse of electronic order after photoexcitation. The results indicate that the dynamics of a structural symmetry-breaking transition are determined by a high-symmetry excited state potential energy surface distinct from that of the initial low-temperature state.