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Administrator<br />

Intermediate status messages may appear in the<br />

Output window. A message appears if the<br />

minimization terminates abnormally, usually<br />

due to a poor starting conformation.<br />

To interrupt a minimization that is in progress:<br />

• Click Stop in the <strong>Com</strong>puting dialog box.<br />

The minimization and recording stops.<br />

Queuing Minimizations<br />

You can start to minimize several models without<br />

waiting for each model to finish minimizing. If a<br />

computation is in progress when you begin<br />

minimizing a second model, the minimization of<br />

the second model is delayed until the first<br />

minimization stops.<br />

If you are using other applications, you can run<br />

minimization with Chem3D in the background.<br />

You can perform any action in Chem3D that does<br />

not change the position of an atom or add or delete<br />

any part of the model. For example, you can move<br />

windows around during minimization, change<br />

settings, or scale your model.<br />

3. Drag in the model window.<br />

A model of Ethane appears.<br />

4. Choose Show Serial Numbers on the Model<br />

Display submenu of the View menu.<br />

You might also want to set the Model Display<br />

Mode to Ball and Stick or Cylindrical Bonds.<br />

5. On the Calculations menu, point to MM2 and<br />

choose Minimize Energy.<br />

6. Click Run on the Minimize Energy dialog box.<br />

The calculation is performed. Messages appear<br />

in the Output Window.<br />

To view all the messages:<br />

• Scroll in the Output Window.<br />

You can also “tear off ” the window and enlarge<br />

it to make it easier to view.<br />

Minimizing Ethane<br />

Ethane is a particularly straightforward example of<br />

minimization, because it has only one<br />

minimum-energy (staggered) and one<br />

maximum-energy (eclipsed) conformation.<br />

To minimize energy in ethane:<br />

1. From the File menu, choose New.<br />

An empty model window appears.<br />

2. Click the Single Bond tool.<br />

The Total Steric Energy for the conformation is<br />

0.8181 kcal/mol. The 1,4 VDW term of 0.6764<br />

dominates the steric energy. This term is due to the<br />

H-H repulsion contribution.<br />

NOTE: The values of the energy terms shown are<br />

approximate and can vary slightly based on the type of<br />

processor used to calculate them.<br />

150•MM2 and MM3 <strong>Com</strong>putations<br />

<strong>CambridgeSoft</strong><br />

Minimize Energy

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