Isotropic periodic sum (IPS) is a technique that calculates long-range interactions differently than conventional lattice sum methods. The difference between IPS and lattice sum methods lies in the shape and distribution of remote images for long-range interaction calculations. The images used in lattice sum calculations are identical to those generated from periodic boundary conditions and are discretely positioned at lattice points in space. The images for IPS calculations are "imaginary", which means they do not explicitly exist in a simulation system and are distributed isotropically and periodically around each particle. Two different versions of the original IPS method exist. The IPSn method is applied to calculations for point charges, whereas the IPSp method calculates polar molecules. However, both IPSn and IPSp have their advantages and disadvantages in simulating bulk water or water-vapor interfacial systems. In bulk water systems, the cutoff radius effect of IPSn strongly affects the configuration, whereas IPSp does not provide adequate estimations of water-vapor interfacial systems unless very long cutoff radii are used. To extend the applicability of the IPS technique, an improved IPS method, which has better accuracy in both homogeneous and heterogeneous systems has been developed and named the linear-combination-based isotropic periodic sum (LIPS) method. This improved IPS method uses linear combinations of basis potentials. We performed molecular dynamics (MD) simulations of bulk water and water-vapor interfacial systems to evaluate the accuracy of the LIPS method. For bulk water systems, the LIPS method has better accuracy than IPSn in estimating thermodynamic and configurational properties without the countercharge assumption, which is used for IPSp. For water-vapor interfacial systems, LIPS has better accuracy than IPSp and properly estimates thermodynamic and configurational properties. In conclusion, the LIPS method can successfully estimate homogeneous and heterogeneous systems of polar molecular systems with good accuracy. © 2012 American Chemical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We sincerely thank Dr. Rio Yokota from King Abdullah University of Science and Technology (KAUST) for fruitful discussions on leading-edge techniques of the tree-based method. K.Z.T. was supported by Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) Fellows 21-5452 of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). T.N. and K.Y. were supported by the Core Research for the Evolution Science and Technology (CREST) of the Japan Science and Technology Corporation (JST). D.S. was supported in part by the Global Center of Excellence Program for “Center for Education and Research of Symbiotic, Safe and Secure System Design” from MEXT.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.