
 Wednesday, March 22, 1995
 Multiperturbation approach to potential energy surfaces
 Published at:Not Found
In Zdependent perturbation theory, the lowestorder wave functions for a polyatomic molecule are
not only independent of the nuclear charges, but also of the total number of nuclear centers and
electrons in the molecule. The complexity of the problem is then determined by the highest order
retained in the calculation. Choosing the simplest possible unperturbed Hamiltonian, we describe an
nelectron, mcenter polyatomic molecule as n ‘‘hydrogenic’’ electrons on a single center perturbed
by electron–electron and electron–nucleus Coulomb interactions. With this H0 , the firstorder wave
function for any polyatomic molecule will be a sum of products of hydrogenic orbitals with either
twoelectron, onecenter or oneelectron, twocenter firstorder wave functions. These firstorder
wave functions are obtained from calculations on Helike and H2
1like systems. Similarly, the
nthorder wave function decouples so that the most complex terms are just the nthorder wave
functions of all the pelectron, qcenter subsystems (p1q5n12) contained in the molecule. We
illustrate applications of this method with some results, complete through third order in the energy,
for H3
1like molecules. These are compared with accurate variational results available in the
literature. We conclude that, through this order, this perturbation approach is capable of yielding
results comparable in accuracy to variational calculations of moderate complexity. The ease and
efficiency with which such results can be obtained suggests that this method would be useful for
generating detailed potential energy surfaces for polyatomic molecules. © 1995 American Institute
of Physics.
J. Chem. Phys. ,Vol. 102 ,No. 12 , 22 March 1995
