Potential curves for several confiirations of polymers consisting of two, thre& five, and six water mo1ecoIe.s have b&n calculated by the extended Hiickel method-. Results for dimers show quaIit&ive agreement with the results of -ab_initio c&uIauons. The methoopredicts non-additivity of the hydrogen bond as the numb& of bonds in the group grows. It is snggested that-several types of bonding exist between water molecules. . Numerous papers [l-11] have already been devoted to theoretical studies of intermolecular energies and _hydrogen~bonding in small polymers of water molecules. Recently, much effort has.beeu put into ab .iuitio calculatious [5-l 11, w-j&h undoubtedly hold the ,kky io understanding the structure of moiecular groupsin water. Theiefore,.our calculations by the program [ 12,131 realizing'the extended Hiickel meth-,' od (the Hoffmauu method) [ 141 are essentially-of methodological value. In fact, it seems reasonable to test the'possibilitiesof the Hoffmann method on .systerns that have been ca&uiated ab initio, which should contribute to a-more ob$ctive estimate-of the results _ -in cases.where ah initio calculations involve d%f&ulties. :GrouBs of water molecules in electroiyte'solution are qualitative.agree&ent with the ab initio results of Del Bene and-Bople [9]. But the extended Htickel -theory (EDT), as considered by, for example, the authors of [1'S]', is not less effective than the CNDO/2 method in certain respects, which is particularly important for us. Thus, Yan et al. [ 151 say that for polypeptides "The CNDO/2 method gives more reliable cited as an example of systems'of interest in the pres-I ent discussion, We hasten to point out in advance, that theresuits of the calculations by the Hoffmarm meth: ' Volume 10, mi&ber 4
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