| level | type of functions | no. of even-tempered Gaussians | 
| 1 | atom-centred s functions | 4 | 
| 2 | atom-centred s functions | 8 | 
| 3 | atom-centred s functions plus one s function (a = 0.5) at midpoint of nearest-neighbour bonds | 8 | 
Table 3
- Quality of auxiliary basis set for the three available levels of accuracy of computational parameter 3.