Millot-Stone potential

Table 4 Importance of Relative Terms in the Millot-Stone Potential for (1-120)2 ... 

Millot C and Stone A J 1992 Towards an aoourate intermoleoular potential for water Mol. Phys. 77 439-62... 

Millot C, Stone AJ (1992) Towards an accurate intermolecular potential for water. Molcular Phys... 

A preliminary molecular dynamics simulation was performed. To this end, SCF-MI and MO-VB calculations were carried out on water dimers and trimers and a new parameterisation of a NCC-like (Niesar-Corongiu-Clementi) [53] potential was accomplished [10d]. The 7s4p2d/4s2p small basis set proposed by Millot and Stone [40] was employed. The Hartree Fock limit results obtained in our previous work were reproduced using this compact basis set also equilibrium geometry and binding energy values compared well with the experimental results. 

As a second model potential we shall briefly discuss the PES for the water dimer. Analytical potentials developed from ab initio calculations have been available since the mid seventies, when Clementi and collaborators proposed their MCY potential [49], More recent calculations by dementi s group led to the development of the NCC surface, which also included many-body induction effects (see below) [50]. Both potentials were fitted to the total energy and therefore their individual energy components are not faithfully represented. For the purposes of the present discussion we will focus on another ab initio potential, which was designed primarily with the interaction energy components in mind by Millot and Stone [51]. This PES was obtained by applying the same philosophy as in the case of ArCC>2, i.e., both the template and calibration originate from the quantum chemical calculations, and are rooted in the perturbation theory of intermolecular forces. 

C. Millot, J-C Soetens, M.T.C. Martins Costa, M.P. Hodges and A.J. Stone, Revised anisotropic site potentials for the water dimer and calculated properties, J. Phys. Chem. A, 102 (1998) 754-770. 

In principle, simulations which use full explicit solvent to account for the natural environment of proteins should give more realistic behavior than those employing any of the above approximations. However, the realization of this in practice depends on the quality of the water model used in the simulation. A simple model that has proven relatively successful in many recent simulations is the TIP3P model for water in which the atoms have fixed charge and fixed relative orientation. More complex models use more points than three to distribute charge or attempt to account for polarization. The most sophisticated water model yet proposed is that by Millot and Stone, which attempts a full description of the relevant physics for intermolecular potentials. Unfortunately, as yet this is too complex to be used in molecular dynamics simulations. 

Interactions between water molecules have been the subject of investigations much more often than any other intermolecular interactions, obviously due to the importance of water in all aspects of hiunan life. An elaborate potential for water using IMPT was developed by Millot and Stone [202] and named ASP. Later an improved version was published [203]. SAPT was used to develop a water dimer potential called SAPT-5s [28-30]. The latter potential and its applications in spectroscopy [29,204,205] and in simulations of liquid water [31,32] have been recently reviewed in [20,21]. Reference [21] also described an improved potential obtained using SAPT(DFT). 

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