INTERMOLECULAR POTENTIAL FOR THE 1,2-DIMETHOXYETHANE-WATER COMPLEX

A method for constructing ab initio polarizable intermolecular potenti als for flexible molecules within the NEMO scheme is presented. In thi s scheme the total interaction energy between two molecules is calcula ted from the properties of the interacting molecules. It is shown that the changes in the charge distribution of a flexible molecule due to conformational changes can be constructed from the interaction of a na tive charge distribution and a set of distributed polarizabilities. It is further shown that this extension of the model results in a straig htforward way to calculate the interaction energy for a given conforma tion (inter- and intramolecular) of a molecular complex. As a test, we have constructed the intramolecular potential for the 1,2-dimethoxyet hane (DME) molecule and the intermolecular potential between a flexibl e DME molecule and water. The potential obtained is compared to the re sults from ab initio quantum chemical calculations at the SCF level fo r the DME-water complex. For the free DME molecule, it is found that a conformation which is anti around all C-C and C-O bonds is favored, w hereas inclusion of a water molecule favors anti-gauche-anti and anti- gauche(+)-gauche(-) around the C-O, C-C, and C-O bonds, respectively.