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AM1 Magnesium parameters

Modelling the bacterial photosynthetic reaction centre:
1. Magnesium parameters for the semiempirical AM1 method developed using a genetic algorithm

Michael C. Hutter, Jeffrey R. Reimers and Noel S. Hush

School of Chemistry F11
University of Sydney

NSW 2006

J. Phys. Chem. B 102 (1998) 8080-8090


Magnesium parameters for use with the semiempirical AM1 method are developed using a specially designed genetic algorithm. Parameterization priorities included development of a robust parameterization capable of describing a wide range of properties in diverse chemical environments, with emphasis on structural features of biologically relevant systems, eg., chlorophylls. Specifically, the test data set included a selection of the heats of formation, geometric properties, dipole moment and ionization energies evaluated for 32 compounds including halides, oxides, hyper valent compounds, organometallics, and porphyrins. In addition, calculated properties for a further 27 molecules are used as an independent test on the quality of the parameterization obtained. Reference data is either taken from experiment, previous ab initio calculations, or evaluated using ab initio or density functional theory. For comparison, analogous results for all 59 molecules are obtained using the semiempirical PM3 and MNDO/d methods. Both AM1 and MNDO/d are found to be robust and widely applicable for magnesium compounds while the applicability of PM3 appears significantly restricted. MNDO/d appears the method of choice for ionization potentials and heats of formation while, reflecting our parameterization priorities, AM1 appears the method of choice for geometrical properties, especially those of magnesium porphyrins.
For information how to include these AM1 Magnesium parameters into common semiempirical program packages like MOPAC, AMPACTM and VAMPTM or GaussianTM please email me.

input examples (in Z-matrix form):

Magnesium porphyrin in fourfold symmetry Mg porphyrin

3. Structural and vibrational properties of bacteriochlorophylls, related porphyrin systems and their radical cations

Michael C. Hutter, Jeffrey R. Reimers and Noel S. Hush


Our published magnesium parameters for use with the semiempirical AM1 method were applied in calculations of properties of porphyrin related species containing magnesium, particularly bacteriochlorophylls. Besides structural investigations on a number of porphyrin derivatives, infra red frequencies and intensities were calculated for neutral and corresponding radical cations of bacteriochlorophyll a, b and methyl-bacteriochlorophyll a, as well as bacteriochlorophyll a with imidazole as an additional ligand.
updated M. Hutter 28. October 1998

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