Pair interaction molecular orbital method: an approximate computational method for molecular interactions

We propose an approximate method for calculating large molecular clusters u sing molecular orbital (MO) methods. The method allows one to obtain the to tal energy of a molecular cluster by performing MO calculations on the mole cules and the molecular pairs in the system. The computational time is grea tly reduced for a system containing a large number of molecules, since the supermolecule calculation of the whole system is avoided. Our method consid ers important terms of many-body interactions within a pair approximation a nd is expected to give results of reasonable accuracy even for molecular in teractions having significant many-body effects. The numerical calculations of water trimers and tetramers revealed that our method included the major portion of the many-body energies. (C) 1999 Elsevier Science B.V. All righ ts resented.