Full counterpoise procedure

The use of the CP correction has generated some controversy related to the use of a full set of ghost orbitals (occupied and virtual) to obtain the BSE energy of the monomers [referred as full counterpoise procedure (FCP)]. Controversy also surrounds a slight variation of the CP in which only the virtual orbitals of the second monomer are used to evaluate the energy of the first monomer, and vice versa. This modification is known as the virtual counterpoise procedure (VCP)." " Some arguments supporting this modification are as follows ... 

Evaluation of the ab initio interaction energy is substantially complicated by the so-called basis set superposition error (BSSE) [57]. This artifact arises from the final size of the basis set and is to be eliminated by the full counterpoise procedure (CP) [58]. The monomer energies are evaluated with the full basis set used for the dimer in the geometry of the complexes (designated E, E ). Then the equation (1) is modified as follows ... 

Since a more complete pointwise scan of the 6D potential was desirable, the total number of calculations amounted to 3284 points. In order to eliminate the remaining BSSE, which even at this level of computation is not negligible, all 3284 points were corrected by applying the full counterpoise procedure. 

Alternate language that one may come across in the literature refers to the process of correcting AT to AE by including the ghost orbitals of each partner as the (Boys-Bernardi) counterpoise procedure.Using the basis set of the full complex at all stages (Eq. 4) is sometimes referred to as the dimer-centered basis set (DCBS) method, whereas discarding the basis functions of the partner for each subunit (Eq. 5) is termed the monomer-centered basis set (MCBS). 

Table 2 explores the aforementioned notion that MP2 serves as a good approximation to full MP4 calculations of H-bond energies. The basis set notation is taken directly from ref. 42, where M refers to a minimal basis set, D to double-C, and Q to quadruple- . The numbers of polarization functions are displayed in the following parentheses. We first focus on the data on the left side of the table, which has been corrected for BSSE by the counterpoise procedure. The full fourth order correction A (4) (AT-(- A -l- A is generally on the order of -0.5 kcal/mol. Note that the minimal type of basis set, even with... 

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