The GAUSSIAN Implementation

To go from a semiempirical calculation in the GAUSSIAN implementation (File 9-1) to an ab initio calculation, one need only change PM3 in the route section of the input file to sto-3g for a single point calculation or sto-3g opt for an optimization. We have made this change in File 10-1 along with the substitution of h for f in the second line of the geometry section to calculate the molecular 

Computational Chemistry Using the PC, Third Edition, by Donald W. Rogers ISBN 0-471-42800-0 Copyright 2003 John Wiley Sons, Inc. 

File 10-1. Input file for an STO-3G ab initio optimization of H2. Exercise 10-1 

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

The input file is File 10-1. The bond length is given in File Segment 10-2. 

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Calculate the bond energy of H J by the G2 method in the GAUSSIAN implementation. 

What is the energy of atomization of Hj in the STO-3G approximation Cany out the calculation in the GAUSSIAN implementation. 

The Gaussian elimination method provides a systematic approach for implementation of the described forward reduction and back substitution processes for large systems of algebraic equations. 

GAUSSIAN implementation with the result found using MP2/6-31G in the route section. 

The basis set used for calculations were the STO-3G, the 3-21G, and the 6-31G basis sets, as implemented by the Gaussian-88 computer program. The energies of interaction were computed by using the supermolecule approach where the sum of the energies of the subsystems are substracted from the energy of the complex. All the species were geometry optimized. 

The Hartree-Fock calculations used the 6-31G basis set as implemented by the Gaussian-86 computer program.55 Protonated and unprotonated species were calculated and the proton affinities were obtained as the difference between the energy of the protonated species and the energy of the unprotonated ones. In addition, 6-31G calculations of the energy, using the 6-31G obtained geometry were performed. 

Gaussian 98M , available in 2002, is an implementation of the Gaussian 98 electronic structure modeling program for the Mac OS X environment. It models a broad range of molecular systems under a variety of conditions, and performs its computations starting from the basic laws of quantum mechanics. 

The nonlocality of the interaction between the quarks in both channels qq and qq is implemented via the same formfactor functions g(q) in the momentum space. In our calculations we use the Gaussian (G), Lorentzian (L) and cutoff (NJL) type of formfactors defined as... 

The electronic structure calculations were carried out using the hybrid density functional method B3LYP [15] as implemented in the GAUSSIAN-94 package [16], in conjunction with the Stevens-Basch-Krauss (SBK) [17] effective core potential (ECP) (a relativistic ECP for Zr atom) and the standard 4-31G, CEP-31 and (8s8p6d/4s4p3d) basis sets for the H, (C, P and N), and Zr atoms, respectively. 

Table 4.2), provides a convenient hierarchy, each model reducing both the errors and the maximum size of the molecule accessible by about a factor of two. A user-friendly implementation of these models is readily available within the Gaussian 98 suite of programs [25]. 

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