Transition state optimization, MOPAC

The semi-empirical molecular orbital calculation software MOPAC in the CAChe Work System for Windows ver. 6.01 (Fujitsu, Inc.) was used in all of calculations for optimization of geometry by the Eigenvector Following method, for search of potential energies of various geometries of intermediates by use of the program with Optimized map, for search of the reaction path from the reactants to the products via the transition state by calculation of the intrinsic reaction coordinate (IRC) [10]. 

In 1983 the first MOPAC program was written and contained both the MlNDO/3 and MNDO models. This program allowed geometry optimization, transition state location by use of a reaction coordinate, gradient minimizations, and vibrational frequency calculations. MNDO has been applied with success to the prediction of polarizabilities, hyperpolarizabilities, ESCA, nuclear quadrupole resonance, and numerous other properties. ... 

All semiempirical calculations were performed on a DEC 7620 computer. Chem-3D Plus on a Macintosh Ilfx was used as a graphical interface for drawing and visualizing all structures and for preparing input files for MOPAC [1]. The transition state structures were localized, optimized, and verified as explained in our previous work [2]. All Density Functional Theory (DFT) computational studies were performed with B3LYP [3] and 6-31G(d) [4] basis set as incorporated into GAUSSIAN [5] computational package. 

Over the next decade MNDO parameters were derived for lithium, beryllium, boron, fluorine, aluminum, silicon, phosphorus, sulfur, chlorine,zinc, germanium, bromine, iodine, tin, mercury, and lead. " In 1983 the first MOPAC program was written, containing both the MINDO/3 and MNDO mediods, which allowed various geometric operations, such as geometry optimization, constrained and unconstrained, with and without symmetry, transition state localization by use of a reaction co-... 

The type and location of donor and acceptor groups on this chromophore that will maximize second order NLO properties is not obvious, however, because the ends of the cyanine chromophore are coordinated to the boron atom and therefore not available for direct modification. A noncentrosymmetric substitution pattern must provide for both a charge transfer transition that is related to the strong absorption in the symmetric molecule and a ground state dipole moment which is substantially parallel to this transition. Candidate structures were therefore evaluated computationally with MOPAC using the AM 1 basis for geometry optimization. Spectroscopic INDO/S methods with configuration interaction (ZINDO) were used for electronic spectra estimation (6). 

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