The Large Quadrupole of Water Molecules
Abstract
Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site modelsmore »
- Authors:
- Publication Date:
- Research Org.:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1042553
- DOE Contract Number:
- AC05-76RL01830
- Resource Type:
- Journal Article
- Journal Name:
- Journal of Chemical Physics
- Additional Journal Information:
- Journal Volume: 134; Journal Issue: 13; Journal ID: ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMPUTERIZED SIMULATION; DIPOLES; ELECTRON DENSITY; ELECTROSTATICS; GEOMETRY; MULTIPOLES; QUADRUPOLE MOMENTS; QUADRUPOLES; SPATIAL DISTRIBUTION; WATER; Environmental Molecular Sciences Laboratory
Citation Formats
Niu, Shuqiang, Tan, Ming-Liang, and Ichiye, Toshhiko. The Large Quadrupole of Water Molecules. United States: N. p., 2011.
Web. doi:10.1063/1.3569563.
Niu, Shuqiang, Tan, Ming-Liang, & Ichiye, Toshhiko. The Large Quadrupole of Water Molecules. United States. https://doi.org/10.1063/1.3569563
Niu, Shuqiang, Tan, Ming-Liang, and Ichiye, Toshhiko. 2011.
"The Large Quadrupole of Water Molecules". United States. https://doi.org/10.1063/1.3569563.
@article{osti_1042553,
title = {The Large Quadrupole of Water Molecules},
author = {Niu, Shuqiang and Tan, Ming-Liang and Ichiye, Toshhiko},
abstractNote = {Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site models to the potential from the QM/MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment},
doi = {10.1063/1.3569563},
url = {https://www.osti.gov/biblio/1042553},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 13,
volume = 134,
place = {United States},
year = {Thu Apr 07 00:00:00 EDT 2011},
month = {Thu Apr 07 00:00:00 EDT 2011}
}