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If you want to …<br />

Then …<br />

watch the minimization<br />

process “live” at each<br />

iteration in the calculation<br />

store each iteration as a<br />

frame in a movie for replay<br />

later<br />

Select Display Every Iteration.<br />

NOTE: Displaying or recording each iteration adds significantly to the time required to<br />

minimize the structure.<br />

Select Record Every Iteration.<br />

view the value of each<br />

measurement in the Output<br />

window<br />

Select Copy Measurements to Output.<br />

restrict movement of a<br />

selected part of a model<br />

during the minimization<br />

Select Move Only Selected Atoms.<br />

Constraint is not imposed on any term in the calculation and the values of<br />

any results are not affected.<br />

NOTE: If you are planning to make changes to any of the<br />

MM2 constants, such as cutoff values or other parameters<br />

used in the MM2 force field, please make a backup copy of<br />

the parameter tables before making any changes. This will<br />

assure that you can get back the values that are shipped with<br />

Chem3D, in case you need them<br />

NOTE: Chem3D guesses parameters if you try to<br />

minimize a structure containing atom types not supported by<br />

MM2. Examples include inorganic complexes where known<br />

parameters are limited. You can view all parameters used in<br />

the analysis using the Show Used Parameters command. See<br />

“Showing Used Parameters” on page 160.<br />

Running a Minimization<br />

To begin the minimization of a model:<br />

• Click Run.<br />

TIP: In all of the following minimization examples,<br />

you can use the MM2 icon on the Calculation toolbar<br />

instead of the Calculations menu.<br />

The Output window appears when the<br />

minimization begins, if it was not already<br />

opened. The data is updated for every iteration<br />

of the computation, showing the iteration<br />

number, the steric energy value at that<br />

iteration, and the RMS gradient. If you have<br />

not selected the Copy Measurements to Output<br />

option, only the last iteration is displayed.<br />

After the RMS gradient is reduced below the<br />

requested value, the minimization ends, and<br />

the final steric energy components and total<br />

appear in the Output window.<br />

<strong>ChemOffice</strong> 2005/Chem3D MM2 and MM3 <strong>Com</strong>putations • 149<br />

Minimize Energy

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