Basis set superposition error BSSE

To remove the BSSE we may consider the use of the basis set ft not only for ab but also for a and This procedure called the counter-poise method, was first introduced by Boys and Bernardi. Application of the full basis set ft when calculating a results in the wave function of A containing not only its own atomic orbitals, but also the atomic orbitals of the ( absent ) partner B, the ost orbitals (Fig. 13.3b). As a by-product, the charge density of A exhibits broken symmetry 

---

Diffuse functions are those functions with small Gaussian exponents, thus describing the wave function far from the nucleus. It is common to add additional diffuse functions to a basis. The most frequent reason for doing this is to describe orbitals with a large spatial extent, such as the HOMO of an anion or Rydberg orbitals. Adding diffuse functions can also result in a greater tendency to develop basis set superposition error (BSSE), as described later in this chapter. 

Corrected for basis set superposition error (BSSE). f Energy in parentheses is calculated at 0 K, the other at 298 K. 

The corrections for basis set superposition errors (BSSE) with the counterpoise correction are still a controversial issue [120-122], However, some type of correction is needed for calculations on systems with weak interactions. It has been proved that only considering the BSSE meaningful results can be obtained on large systems [122], Of course, by using good quality basis sets the BSSE is less troublesome and the results obtained can be accepted, readily, as reliable. The BSSE in DFT calculations is less important than in conventional ab-initio calculations. We compute the counterpoise correction as ... 

Table 5. The Basis Set Superposition Error (BSSE) for CH5(H2). The Monomers in Parentheses are Ghost Molecules. " AE Indicates the Difference between the Energy of the Monomer within the Monomer vs. the Dimer Basis...

As it is well known, the Basis Set Superposition Error (BSSE) affects calculations involving hydrogen bonds [1] and, more generally, intermolecular interaction investigations [2,3], This issue of consistency, as first pointed out in 1968 [4], arises from the use of an incomplete basis set but it does not correspond to the basis set truncation error and it is due to the use of diffuse functions on neighbouring interacting particles, which leads to a non physical contribution to the interaction energy within the complex. 

Special attention has been dedicated to the study of the basis set superposition error (BSSE). The SCF-Ml algorithm which excludes the BSSE from the SCF function was employed. A multi configuration version of it, particularly suited to study proton transfer effects, has been formulated. The use of these techniques has led to binding energy values which show a better stability against variation of the basis set, when compared with standard SCF results. For a more complete evaluation of the advantages of the a priori strategy to avoid BSSE see references [47-50], where applications to the study of the water properties are reported, and reference [51], where the Spin Coupled Valence Bond calculations for the He-LiH system are presented. 

The Effect of Basis Set Superposition Error (BSSE) on the Convergence of Molecular Properties Calculated with the... 

In the present work we summarize and continue a systematic study on van der Waals (vdW) interacting molecules using separated molecular orbitals (SMOs). Since the avoidance of basis set superposition error (BSSE) ([1] and reference therein) turned out to be one of the main problems in the study of vdW systems, we pay special attention to this question. It is known that the counter-poise (CP) method [2] is often used in order to correct the BSSE. 

In addition to the cluster calculations, we report details of recent first-principles calculations based on the density functional formalism. These calculations employ periodic boundary conditions to allow investigation of the entire zeolite lattice, and therefore the use of a plane-wave basis set is applicable. This has a number of advantages, most notably that the absence of atom-centered basis functions results in no basis set superposition error (BSSE) (272), which arises as a result of the finite nature of atom-centered basis sets. Nonlocal, or gradient, corrections are applicable also, just as they are in the cluster calculations. 

---