Monte Carlo simulations of water clusters on a parallel computer using an ab initio potential

Abstract

ABSTRACT:We performed a simulation of a cluster of five water molecules at 300 K using an ab initio potential. In our first study, the interactions were calculated at the U Ž . Hartree᎐Fock level using a 6-31G basis set. A parallel big move hybrid Monte Carlo algorithm was used to conduct this modeling. We compared the results obtained for this ''quantum'' system with those obtained from a conventional simulation employing an effective pair potential. We also estimated properties of the quantum system in terms of the configurations generated by the conventional simulation by employing the appropriate Boltzmann weighting. These estimates are in good agreement with those obtained from the full quantum simulation. We then repeated the Boltzmann weighting method, but this time using the BLYP density functional in our ab initio calculations, so as to include correlation effects.

Structure of cyanobacterial Photosystem I

“…Five water molecules located in a pocket at the A-branch, which show a non-specific arrangement. In contrast, five of the total of six water molecules located between the quinone-binding pocket and FX at the B-branch phylloquinone form the structure of a hexagon, which is a well defined low energy arrangement of a water cluster (Akhmatskaya et al 1999). This hexagon structure of the water cluster at the B-branch may also contribute to the lowering of the reorganization energy and the activation energy barrier at the B-branch.…”

Physicochemical Properties of Hydrated Complexes in the Earth's Atmosphere

“…Weakly bound complexes containing water have generated substantial scientific interest. ,,− Water, in all of its phases, is a major player in the absorption of solar and terrestrial radiation. , Because of this, complexes that contain water have great potential to alter the radiative balance and chemistry of our atmosphere. It is well-known that water is able to form complexes with both itself and with other atmospheric chromophores. ,,,,,− ,,,− ,− ,− …”

“…Through the use of innovative experimental techniques and complex ab initio calculations, a wealth of structural, dynamical, and energetic information has been generated for numerous hydrated complexes. Recent studies have focused on O 2 −H 2 O, ,− N 2 −H 2 O, ,− H 2 −H 2 O, − CO−H 2 O, ,,− Cl 2 −H 2 O, CO 2 −H 2 O, , NH 3 −H 2 O, ,,, NO x −H 2 O, ClO x −H 2 O, , HOCl−H 2 O, , O 3 −H 2 O, ,,, (H 2 O) n , ,,,,,, H 2 S−H 2 O, HO x −H 2 O, , SO 3 −H 2 O, ,, HNO 3 −H 2 O, , H 2 CO−H 2 O, − and (CH 3 ) 2 CO−H 2 O …”

Structural changes in the water tetramer. A combined Monte Carlo and DFT study

“…It is not surprising that high-level quantum chemistry calculations have not been coupled with thermodynamic simulations of water clusters at non-zero temperatures, for which dozens of millions of configurations have to be included to obtain converged data. With a few exceptions, [13][14][15] simple and computationally cheap empirical potentials have been usually employed in thermodynamic simulations, even for the relatively small water tetramer. [16][17][18] These potentials were originally developed for the modelling of bulk water properties and are thus only of limited use for aggregates containing a few to a few dozens of molecules.…”