STO-3G basis sets

Because th e calculation of m n Iti-ceiiter in tegrals that are in evitable for ah iniiio method is very difficult and time-con sum in g. Ilyper-Chem uses Gaussian Type Orbital (GTO) for ah initio methods. In truly reflecting a atomic orbital. STO may he better than GTO. so HyperC hem uses several GTOs to construct a STO. The number of GTOs depends on the basis sets. For example, in the minimum STO-3G basis set IlyperGhem uses three GTOs to construct a STO. 

In eonPast to the low-Ievel ealeulations using the STO-3G basis set, very high level ealeulations ean be earried out on atoms by using the Complete Basis Set-4 (CBS-4) proeedure of Petersson et al. (1991,1994). For atoms more eomplieated than H or He, the first ionization potential (IP[) ealeulation is a many-eleePon ealeulation in which we ealeulate the total energy of an atom and its monopositive ion and determine the IP of the first ionization reaetion... 

Calculate the H—H bond length in ground-state H2 using the STO-3G basis set in the GAUSSIAN for Windows implementation. 

Minimal basis sets use fixed-size atomic-type orbitals. The STO-3G basis set is a minimal basis set (although it is not the smallest possible basis set). It uses three gaussian primitives per basis function, which accounts for the 3G in its name. STO stands for Slater-type orbitals, and the STO-3G basis set approximates Slater orbitals with gaussian functions. ... 

The presence of a single polarization function (either a full set of the six Cartesian Gaussians dxx, d z, dyy, dyz and dzz, or five spherical harmonic ones) on each first row atom in a molecule is denoted by the addition of a. Thus, STO/3G means the STO/3G basis set with a set of six Cartesian Gaussians per heavy atom. A second star as in STO/3G implies the presence of 2p polarization functions on each hydrogen atom. Details of these polarization functions are usually stored internally within the software package. 

The STO-3G basis set is clearly inadequate for such calculations. The results demonstrate the importance of the diffuse functions and electron correlation. The density functional results are very attractive. 

The details of the functional form and parameterization have not yet been published. The advantage is that basis sets involving d-orbitals are readily included (defining the SAMID method), making it possible to perform calculations on a larger fraction of the periodic table. The SAMI method explicitly uses the minimum STO-3G basis set, but it is in principle also possible to use extended basis sets with this model. The acmal calculation of the integrals makes the SAMI method somewhat slower than the MNDO/ AM1/PM3, but only by a factor of 2. The SAMI/SAMID methods have been parameterized for the elements H, Li, C, N, O, F, Si, P, S, Cl, Fe, Cu, Br and 1. 

Semiempirical AMI and ab initio calculations using GAUSSIAN 86 with the STO-3G basis set were used to explain the site of alkylation in compounds 1... 

A new period in theoretical work on arenediazonium ions began with Vincent and Radom s paper in 1978. This was the first ab initio study of the methane- and benzenediazonium ions, and was carried out with a minimal (STO-3G) basis set, subject only to some (specified) symmetry constraints and a fixed CH bond length (108.3 pm). The optimized structure of the benzenediazonium ion is given in Figure 4-2. 

Arising from studies of the photochemistry of benzenesulfonyl systems, extensive ab initio MO calculations have been made for various sulfonyl radicals and related species253. The STO-3G basis set, which includes d-type polarization functions on second-row atoms, was used. The inclusion of d orbitals on sulfur was found to be very... 

It is feasible to carry out Hartree-Fock calculations on our available computer resources (an SGI Crimson Elan Workstation) using an STO-3G basis set with full geometry optimization of CeoMu but only partial geometry optimisations of the ChoMu isomers. Fig. 1 shows planar graphs of Ceo and C70 with the carbon atoms suitably labelled for future reference. 

Whereas there are only two different bond lengths in Ceo, short between atoms 1 and 2 and long between atoms 2 and 3, there are seven different bond lengths in C. The Crobond lengths have been calculated here and previously [12] by the restricted Hartree-Fock method using an STO-3G basis set and are discussed in some detail... 

Scheme 7.25 shows the role of quinone methide energy on the cation-quinone methide equilibrium. A high pKa value for this equilibrium is expected if the energy of the quinone methide approaches that of the carbocation. To construct this cycle, we used the Ka values that we determined for the protonated ketone (pKa — —0.9) and quinone methide (pKa = 6.6). This pKa difference requires that the keto form be more stable than the quinone methide by — 10.2kcal/mol. We obtained the calculated energy difference of lO.lkcal/mol from Hartree-Fock calculations using 6-31G and STO-3G basis sets, inset of Scheme 7.25. 

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