Quantum Monte Carlo benchmark energies of water systems

There is ample evidence that the diffusion Monte Carlo (DMC) technique is very accurate for non-covalent interactions. Comparisons with energy benchmarks provided by the couple-cluster technique CCSD(T) suggest that DMC is often competitive in accuracy [1-5]. However, the computational scaling of DMC with system size is far more favorable than that of CCSD(T), so that DMC can provide valuable energy benchmarks for rather large systems, including periodic systems representing extended crystals and liquids.

It is planned that this page will provide DMC benchmark energies for a number of water systems, including clusters, ice structures and liquid water. The data files have standard xyz format, with each file containing atomic coordinates and energies for a set of configurations for a given system. The block of data for each configuration consists of the following lines:

Line 1 : number of atoms N

Line 2 : DMC energy of the configuration

Lines 3, ... N+2 : chemical symbol and x, y, z coordinates of each of the N atoms

The DMC energy is the energy per monomer of the system (eV units) relative to the energy of the appropriate number of isolated water molecules in free space, the free molecules being in the equilibrium geometry computed in Ref. [6]. (In this geometry, the O-H bond length is 0.95865 Angstrom and the H-O-H bond angle is 104.348 deg.) DMC energies are subject to a statistical (sampling) error, and the value of this is also given in line 2. This is the rms sampling error of the total energy divided by the number of monomers. The x, y, z coordinates are in Angstrom units.

[1] I. G. Gurtubay and R. J. Needs, J. Chem. Phys. 127, 124306 (2007).

[2] B. Santra, J. Klimes, D. Alfè, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011).

[3] M. J. Gillan, F. R. Manby, M. D. Towler, and D. Alfè, J. Chem. Phys. 136, 244105 (2012).

[4] F.-F. Wang, M. J. Deible, and K. D. Jordan, J. Phys. Chem. A 117, 7606 (2013).

[5] M. Dubecky, P. Jurecka, R. Derian, P. Hobza, M. Otyepka, and L. Mitas, J. Chem. Theory Comput. 9, 4287 (2013).

[6] H. Partridge and D. W. Schwenke, J. Chem. Phys. 106, 4618 (1997).

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The following configurations come from D Alfè, A. P. Bartok, G. Csanyi and M. J. Gillan, J. Chem. Phys. 141, 014104 (2014).

Compressed Nonamer.

Compressed Pentadecamer.

Compressed Icosiheptamer.

Water 32 molecules, BLYP configurations, rho=1.245 g/cm^2,T=420K.

Water 32 molecules, BLYP-2 configurations, rho=1.245 g/cm^2,T=420K.

Water 32 molecules, PBE configurations, rho=1.245 g/cm^2,T=420K.

Water 32 molecules, PBE-2 configurations, rho=1.245 g/cm^2,T=420K.

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The following configurations were used in D Alfè, A. P. Bartok, G. Csanyi and M. J. Gillan, J. Chem. Phys. 138, 221102 (2013), they have been generated by E. R. Hernandez using the q-TIP4P/F model (see S. Habershon, T. E. Markland and D. E. Manolopoulos. J. Chem. Phys. 131, 024501 (2009)) as implemented in the ARCE code developed by R. Ramirez.

Water 32 molecules rho=0.997 g/cm^2,T=300K.

Water 64 molecules rho=0.997 g/cm^2,T=300K.

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The following configurations come from B. Santra, J. Klimes, D. Alfè, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, M. Sheffler, Phys. Rev. Lett. 107, 185701 (2011)

Ice Ih, rho=0.9379 g/cm^2.

Ice II, rho=1.197 g/cm^2.

Ice VIII, rho=1.567 g/cm^2.

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The following configurations come from R. Zamann, D. Alfè, C. G. Salzmann, J. Klimes, A. Michaelides and B. Slater, Phys. Chem. Chem. Phys. 13, 19788 (2011)

Ice XIh, rho=1.009 g/cm^2.

Ice XIc, rho=1.009 g/cm^2.

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The following configurations come from M. J. Gillan, D. Alfè, F. R. Manby, J. Chem. Phys. 143, 102812 (2015). The files contain the total energy of the clusters, and the binding energies of a single methane molecule inside the respective water clusters computed as the difference between the energy of the cluster and the energy of the same system with the methane molecule moved 10 A away.

CH4-H2O dimer.

CH4-(H2O)5 cluster.

CH4-(H2O)10 cluster.

CH4-(H2O)15 cluster.

CH4-(H2O)20 cluster.


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