SPARTAN program

Another important consideration is the amount of labor necessary on the part of the user. One major difference between different software packages is the developer s choices between ease of use and efficiency of operation. For example, the Spartan program is extremely easy to use, but the price for this is that the algorithms are not always the most efficient available. Many chemistry users begin with software that is very simple, but when more sophisticated problems need to be solved, it is often easier to learn to use more complicated software than to purchase a supercomputer to solve a problem that could be done by a workstation with different software. 

The conformation with the lowest found energy from the previous conformational analysis was subjected to a geometry optimization (energy minimization) using the semi-empirical quantum chemistry-based AMI method available in the Spartan program. 

A quantum mechanical ab initio calculation using a 3-21G basis set without further geometry optimization (single point calculation) was subsequently performed on all AMI optimized (minimized) conformations using the Spartan program. 

Many other approaches for finding a correct structural model are possible. A short description of ab-initio, density functional, and semiempirical methods are included here. This information has been summarized from the paperback book Chemistry with Computation An Introduction to Spartan. The Spartan program is described in the Computer Software section below.65 Another description of computational chemistry including more mathematical treatments of quantum mechanical, molecular mechanical, and statistical mechanical methods is found in the Oxford Chemistry Primers volume Computational Chemistry,52... 

Fig. 6.9 Atom charges and bond orders calculated using the AMI, PM3 and HF/3-21G( ) methods. In a and b the charges and bond orders are all from the Mulliken approach. In c and d the charges are all electrostatic potential charges, and the bond orders are Mulliken for AMI and PM3, and Lowdin for HF/3-21G< ) (Lowdin bond orders were not available for AMI and PM3 from the Spartan program used). Note that charges and bond orders involving hydrogens have been omitted...

These books, oriented toward Wavefunction s Spartan program, are very useful introductions to the practice of computational chemistry, particularly to practical methods of getting useful results. 

Semi-empirical and ab initio studies have been used to examine the stereospecifities of adducts from the Ru-catalyzed [2ji+2ji] cycloaddition of 5-azabicyclo[2.2.0]hex-2-en-6-one as a dienophile with cyclobutadiene and cyclopentadiene. The study was conducted at the semi-empirical (AMI and PM3) and ab initio (STO-3G-21G, 6-31G, MP2/6-31G ) levels of theory employing the SPARTAN program version 4.1.1. The predictions made by ab initio calculation were in agreement with the experimental results <1997SL38>. 

Double click on the Spartan shortcut icon on the desktop. This should open the Spartan program and you should have a blank, workspace window in front of you. 

An aid to finding the reactants and products for a given transition state is the fact that the atomic displacements in the normal vibrational mode that corresponds to the imaginary frequency tend to be in the directions of the reactants and products for this transition state. In the SPARTAN program, one can produce an animation of this mode. 

The PM3 method has been extended by the developers of the SPARTAN program (Section 15.15) to include d orbitals for many transition metals, giving the method PM3(tm), which is available in SPARTAN (www.wavefun.com). 

Fig. 2.5 Visualizing the electrostatic potential around pyramidane reveals the presence of a lone pair on the apical carbon (calculations with the Spartan program). For comparison, methylene, CH2, is shown...

Tills section will describe how to predict NMR spectrum using the Spartan program. We will predict NMR of the spiro compound 2 using the HF method with 6-3IG basis set. First, the software performs the job of geometry optimization and then calculates the NMR parameters. The stracture is initially built using the build option (Fig. 7.19). 

Q-Chem (www.q-chem.com) is an ab initio package for computers using UNIX or LINUX and can also be run on Windows and Macintosh machines by using the Spartan program (see below) as a front end. Q-Chem allows calculations on large molecules and can do Hartree-Fock, MP, CC, and density-functional calculations [Y. Shao et al., Phys. Chem. Chem. Phys., 8, 3172 (2006)]. It incorporates methods such as CFMM and ONX to achieve linear scaling (Section 15.16) for large molecules. 

For the Spartan program (only), the NBO program provides a SPARTAN keyword option, namely,... 

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