Effects of basis set and electron correlation on the calculated properties of the ammonia dimer
- 1 July 1984
- journal article
- conference paper
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 81 (1) , 407-409
- https://doi.org/10.1063/1.447319
Abstract
Ab initio calculations are carried out for (NH3)2 with a 6‐31G**(1p,2d) basis set containing diffuse polarization functions. Electron correlation is included via second‐order Mo/ller–Plesset perturbation theory (MP2). At the SCF level, the equilibrium R(NN) distance is 3.54 Å and the interaction energy is −2.35 kcal/mol. Inclusion of correlation enhances the attraction substantially, increasing the energy to −4.05 kcal/mol and reducing the intermolecular separation by 0.20 Å. Comparison with previous results at the SCF level demonstrates a variety of errors including exaggerated dipole moments, underestimation of polarization energy, and sizable superposition errors with these smaller basis sets.Keywords
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