A systematic study on the basis set superposition error in the calculation of interaction energies of systems of biological interest

Abstract

A systematic study on the basis set superposition error in the calculation of interaction energies of strongly bonded molecular associations is presented. Twenty-four different basis sets (ranging from minimal to triple-zeta plus polarization) have been used to compute the interaction energies of four conformations of two alanine molecules interacting through their respective carboxylic groups giving rise to a double hydrogen-bonded association. The basis set superposition error has been calculated in all the cases by using the functional counterpoise method of Boys and Bernardi. It is shown that the basis set superposition error is still important at the double-zeta and valence triple-zeta levels of accuracy. In most cases the correction by the counterpoise method seems to be adequate providing interaction energies which, when compared with the uncorrected ones, are in better agreement with those coming from the largest basis set used in this work ( full triple-zeta plus polarization). The use of basis sets which have a relatively small basis set superposition error (GEOLARGE, GEOTRIPLEZ, 6-31G**, 6-31G**++(ss) , 13,8/5,3*], [13,8/5,3**], and GEOTRIPLEZ**) in projects involving systems of biological interest, require both, computational time and storage capacity, which by far exceed what is generally affordable. The use of appropriately designed minimal basis sets together with the counterpoise correction constitutes a reasonably good approach to such systems.