Ab initio programs

Werner HJ, Knowles PJ, Lindh R, Schiitz M, Celani P, Korona T, Manby FR, Rauhut G, Amos RD, Bemhardsson A, Beming A, Cooper DL, Deegan MJO, Dobbyn AJ, Eckert F, Hampel C, Hetzer G, Lloyd AW, McNicholas SJ, Meyer W, Mura ME, Nicklass A, Palmieri P, Pitzer R, Schumann U, Stoll H, Stone AJ, Tarroni R, Thorsteinsson T (2003) Molpro, version 2002.6, a package of ab initio programs... 

MOLPRO is a suite of ab initio programs written by H.-J. Werner and P. J. Knowles, with contributions from J. Almlof, R. D. Amos, A. Berning... 

A practical guide and tutorial to the ab initio program Gaussian. 

Ab-initio CAChe features all of the above plus ab-initio and density functional methods. This program requires a workstation (Windows NT minimum or SGI and IBM unix-based machines) and can be used to build and visualize results from ab-initio programs (e.g., Gaussian, see description under Gaussian, Inc.). Also, CAChe directly interfaces to Dgauss , a computational chemistry package that uses density functional theory to predict molecular structures, properties, and energetics. 

The matrix elements of the momentum operator in (12) are now written in terms of derivative overlap integrals which can be obtained from the gradient package. These integrals are standard available in Ab Initio programs capable of performing a geometry optimisation. 

In the late 1970s no ab initio programs contained algorithms for directly computing IR frequencies or intensities. However, two groups independently (Kollmar and Staemmler and Hess and Schaad ) undertook the calculation of the IR spectrum of 1. This required a point-by-point calculation of the force-constant matrix, but fortunately the high symmetry (D2 ) of cyclobutadiene significantly... 

M0LPR094 is a suite of ab initio programs written by Werner, H.-J. and... 

Three isomeric structures were predicted for [ZnCp] ions. The most stable was determined to be the /7 -bound isomer. The z - and -bound structnres were ca 0.14 and 0.35 eV higher in energy than the z -bound isomer. All structures were optimized using a package of ab initio programs. For the [ZnCp] ion, only the /j -bonnd strnctnre has been examined. ... 

In practical terms, a post-HF method (38) that is able to reliably optimize ground and excited states must be used. One such method is CASSCF, which is available in ab initio programs such as Gaussian. The drawback of modeling with a post-HF method is that the computer time requirements are heavy. Molecules with 10-15 first-row atoms are about as large as can be handled accurately. 

The arrival of ab initio programs based on Gaussian-type orbitals and more powerful computers reduced all these developments to historical souvenirs. It should be emphasized, however, that Sandorfy s work constituted the first attempt to go beyond the 7t-electron approximation, and the first molecular orbital treatment of polyatomic molecules that took into account all valence electrons without using group orbitals. 

It should be realized modem ab initio programs do not rigidly follow the basic SCF procedure described in this section. To speed up calculation they employ a... 

The electron distribution around an atom can be represented in several ways. Hydrogenlike functions based on solutions of the Schrodinger equation for the hydrogen atom, polynomial functions with adjustable parameters, Slater functions (Eq. 5.95), and Gaussian functions (Eq. 5.96) have all been used [34]. Of these, Slater and Gaussian functions are mathematically the simplest, and it is these that are currently used as the basis functions in molecular calculations. Slater functions are used in semiempirical calculations, like the extended Hiickel method (Section 4.4) and other semiempirical methods (Chapter 6). Modem molecular ab initio programs employ Gaussian functions. 

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