Geometrical basis sets

This universal even-tempered basis set was employed in all of the correlation energy calculations summarized in Table VII. Clement and his collaborators have investigated the use of this type of basis set within the Hartree-Fock approximation. They impose the further restriction of using the same exponents for all values of / and term such basis sets geometric basis sets . Huzinaga comments that these remarkable universal geometric basis sets... will certainly usher us to a new plateau of computational chemistry. ... 

Clementi, E., and Corongiu, G., Geometrical Basis Sets for Molecular Computations, IBM Research Report, Poughkeepsie, 1982. 

Y. Ishikawa, G. L. MaUi, A. J. Stacey. Matrix Dirac-Fock-Breit SCF calculations on heavy atoms using geometric basis sets of Gaussian functions. Chem. Phys. Lett., 188(1,2) (1992) 145-148. 

The concepts of even-tempered exponents and universal basis sets were combined along with six constraints to produce geometrical basis sets for all atoms from H to Sr. The same set of exponents (but differing numbers of s, p, and d functions) appears. Errors in the atomic energies range from 0.0002 hartree for the 6s hydrogen basis to 0.0005 hartree for the (I3s,8p) carbon basis to 0.0555 hartree for the (20s,13p,8d) Sr basis. 

E. dementi and G. Corongiu, Chem. Phys. Lett., 90,359 (1982). Geometrical Basis Set for Molecular Computations. 

Figure 3 shows the results with and without including the geometric phase effect for the D + H2 reaction. The basis set is taken as 1,1,1,15,15,15, that is. 

Even-tempered basis sets (M. W. Schmidt and K. Ruedenberg, J. Chem. Phys. 71, 3961 (1979)) consist of GTOs in which the orbital exponents ak belonging to series of orbitals consist of geometrical progressions ak = a, where a and P characterize the particular set of GTOs. 

Geometric properties are quite sensitive to the basis set chosen, including the presence or absence of polarization functions (additional s and -type functions on H and on heavy atoms). 

Figure 1.1 Transition state for methyl radical addition to ethylene. Geometric parameters are from ab initio calculation with QCISD(T)/6-31GT(d) basis set.29...

Table III displays VEDEs obtained with the Brueckner-reference methods discussed in Section 5.2 and augmented, correlation-consistent, triple- basis sets [41]. AEDEs include zero-point energy differences and relaxation energies pertaining to geometrical relaxation on the neutral s potential energy surface. The average absolute error with respect to experiment is 0.05 eV [26].

The results of the geometry optimizations are shown in Table 1. With some minor deviations, the geometrical parameters agree well with those of ref. [9], One can also note that, as already mentioned, the geometries obtained using the 6-3 lG(d) and 6-31 lG(d,p) basis sets, respectively, are very similar. 

Table 1 Optimized Geometrical Parameters for the Benzene Radical Cation Ground State ( B3g), Obtained Using B3-LYP with Various Basis Sets.

To investigate the basis set effect in connection with geometric strain in BF, we have performed calculations with and without d-type functions on corannulene. The d-functions improve the binding with about 10 kcal/mol per C-atom in C20H10 the corresponding improvement in coronene (C24H 2) 8 kcal/mol. 

Fig. 5.16 Calculated structure of ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), resulting from geometric optimization with the B3LYP functional and 6-3IG -I- VTZ basis set [101]. Color scheme cyan = iron, green = carbon, blue = nitrogen, red = oxygen (taken from [101])...

Basis Set Choice The most relevant geometrical parameters of several stationary points, with and without an explicit water molecule, located using several... 

---