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Quality<br />

The quality of a parameter indicates the relative<br />

accuracy of the data.<br />

Quality Accuracy Level<br />

1 Parameter guessed by Chem3D.<br />

2 Parameter theorized but not<br />

confirmed.<br />

3 Parameter derived from<br />

experimental data.<br />

4 Parameter well confirmed.<br />

Reference<br />

The reference for a measurement corresponds to a<br />

reference number in the References table.<br />

References indicate where the parameter data was<br />

derived.<br />

Estimating<br />

Parameters<br />

In certain circumstances Chem3D may estimate<br />

parameters.<br />

For example, during an MM2 analysis, a non-MM2<br />

atom type is encountered in your model. Although<br />

the atom type is defined in the Atom Types table,<br />

the necessary MM2 parameter will not be defined<br />

for that atom type. For example, torsional<br />

parameters are missing. This commonly occurs for<br />

inorganic complexes, which MM2 does not cover<br />

adequately. More parameters exist for organic<br />

compounds.<br />

In this case, Chem3D makes an educated “guess”<br />

wherever possible. A message indicating an error in<br />

your model may appear before you start the<br />

analysis. If you choose to ignore this, you can<br />

determine the parameters guessed after the analysis<br />

is complete.<br />

To view the parameters used in an MM2 analysis:<br />

• From the Calculations menu, point to MM2,<br />

and choose Show Used Parameters.<br />

Estimated parameters have a Quality value of<br />

1.<br />

Creating Parameters<br />

The MM2 force field parameters are based on a<br />

limited number of MM2 atom types. These atom<br />

types cover the common atom types found in<br />

organic compounds. As discussed in the previous<br />

section, parameters may be missing from structures<br />

containing other than an MM2 atom type.<br />

NOTE: Adding or changing parameter tables is not<br />

recommended unless you are sure of the information your are<br />

adding. For example, new parameter information that is<br />

documented in journals.<br />

NOTE: A method for guessing at missing MM2<br />

Parameters can be found in “Development of an Internal<br />

Searching Algorithm for Parameterization of the<br />

MM2/MM3 Force Fields”, Journal of <strong>Com</strong>putational<br />

Chemistry, Vol 12, No. 7, 844–849 (1991).<br />

To add a new parameter to a parameter table:<br />

1. From the View menu, point to Parameter Tables<br />

and choose the parameter table to open.<br />

The parameter table appears.<br />

2. Right click on a row header and choose<br />

Append Row from the context menu.<br />

A blank row is inserted.<br />

Appendices<br />

<strong>ChemOffice</strong> 2005/Appendix Parameter Tables • 651<br />

Estimating Parameters

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