Quantifying Intramolecular Basis Set Superposition Errors

We show that medium-sized Gaussian basis sets lead to
significant
intramolecular basis set superposition errors at Hartree–Fock
and density functional levels of theory, with artificial stabilization
of compact over extended conformations for a 186 atom deca-peptide.
Errors of ∼80 and ∼10 kJ/mol are observed, with polarized
double zeta and polarized triple zeta quality basis sets, respectively.
Two different procedures for taking the basis set superposition error
into account are tested. While both reduce the error, it appears that
polarized quadruple zeta basis sets are required to reduce the error
below a few kJ/mol. Alternatively, the basis set superposition error
can be eliminated using multiresolution methods based on Multiwavelets.