No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
The full text of this article is not currently available.
Energy benchmarks for methane-water systems from quantum Monte Carlo and second-order Møller-Plesset calculations
22.L. Jensen, K. Thomsen, N. von Solms, S. Wierzchowski, M. R. Walsh, C. A. Koh, E. D. Sloan, D. T. Wu, and A. K. Sum, J. Phys. Chem. B 114, 5775 (2010).
41.T. Helgaker, P. Jorgensen, and J. Olsen, Molecular Electronic Structure Theory (Wiley, New York, 2000).
68.R. J. Needs, M. D. Towler, N. D. Drummond, and P. López-Ríos, Casino 2.12 User Manual, 2013.
74.H.-J. Werner et al.
, version 2012.1, a package of ab initio
programs, 2012, see http://www.molpro.net
75.H. J. Werner, P. J. Knowles, G. Knizia, F. R. Manby, and M. Schutz, Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2, 242 (2012).
84. Since we use BLYP without correcting for non-local electron correlation (dispersion), an accurate approximation to the real-world system is not necessarily expected. However, our aim here is simply to create a set of CH4-H2O configurations spanning a wide range of C-O separations and molecular orientations.
85. We take the equilibrium O–H bond length and H-O-H angle in the H2O monomer to be 0.958 Å and 104.5°, and the C–H bond-length in the CH4 monomer to be 1.088 Å. The equilibrium geometry of the H2O monomer is restored in two steps: first, the O–H bonds are restored to their equilibrium length, keeping their direction fixed; second, the H-O-H angle is restored to its equilibrium value, keeping the direction of the H-O-H bisector fixed. The position of the O atom is held fixed throughout. For the CH4 monomer, a sequence is adopted for the four H atoms, and the same procedure as for the H2O monomer is applied to the first two H atoms. The lengths and directions of the other two C–H bonds are then adjusted to give the tetrahedral equilibrium geometry.
88. For large Rc, the residual error is approximately proportional to the 3-dimensional integral of 1/r6 over the region lying beyond the radius Rc, this integral being .
Article metrics loading...
The quantum Monte Carlo (QMC) technique is used to generate accurate energy benchmarks for methane-water clusters containing a single methanemonomer and up to 20 watermonomers. The benchmarks for each type of cluster are computed for a set of geometries drawn from molecular dynamics simulations. The accuracy of QMC is expected to be comparable with that of coupled-cluster calculations, and this is confirmed by comparisons for the CH4-H2O dimer. The benchmarks are used to assess the accuracy of the second-order Møller-Plesset (MP2) approximation close to the complete basis-set limit. A recently developed embedded many-body technique is shown to give an efficient procedure for computing basis-set converged MP2 energies for the large clusters. It is found that MP2 values for the methane binding energies and the cohesive energies of the water clusters without methane are in close agreement with the QMC benchmarks, but the agreement is aided by partial cancelation between 2-body and beyond-2-body errors of MP2. The embedding approach allows MP2 to be applied without loss of accuracy to the methane hydrate crystal, and it is shown that the resulting methane binding energy and the cohesive energy of the water lattice agree almost exactly with recently reported QMC values.
Full text loading...
Most read this month