gaussian基本概念和用法(16)

the model chemistry. Save 6.Click okay 7.Submit

It's also a good idea to add the keyword \can compare to what you are trying to include, to make sure that everything was read in correctly.

Freezing A Parameter

1.Draw molecule as normal - using gaussview 2.Select 'Gaussian' on the 'calculate' menu

3.Select the usual parameters in the calculation setup dialog box 4.In the 'additional keywords' box type 'opt=modredundant' 5.Click edit

6.At the end of the geometry specification type the parameter that you want to freeze, e.g. for a dihedral angle it could be '1 2 3 4 165. F' 165 is the angle that you want to freeze it at (don't forget the full stop!). G98 knows it is a dihedral as there are 4 atoms specified. Do this for each parameter that you want to freeze - do each on a new line with no blank lines between them. Make sure that you leave a blank line between the sets of text i.e. the geometry specification and any other text that was there beforehand. Save 7.Then click okay 8.Submit

Choosing a dihedral value very different from the input geometry can cause problems (Gaussian will crash and tell you that 'it couldn't resolve a coordinate'). If this happens, it might be better to try the option of doing a relaxed potential energy surface scan. Essentially this is the same as doing optimizations at a series of frozen values of a given coordinate. For example, replacing \2 3 4 165. F\with \2 3 4 180. S 15 -5.\would do 15 geometry optimizations. The first optimization with the dihedral at 180, then 175, etc in increments of -5 degrees. A summary of the scan is placed at the end of the log file.

Setting Up A Batch File

Lets say that you have four different calculations that you want to perform, they will be named test1, test2, test3 and test4. Set up the calculations as would like them to be performed, but when you get to the final 'submit' box you can cancel the calculation. You will now have four .gjf files with the appropriate names. 1.Open G98W and click on 'utilities', 'edit batch file', a dialogue box opens. 2.Click on 'add'.

3.Type in your first filename test1.gjf, (make sure that you include the file extension .gjf as otherwise you will get an error message later) click 'ok'.

4.G98W suggests the appropriately named *.out file name, click 'ok'. 5.Click 'add' and repeat the procedure for each of your four files.

6.When all you files have been entered, click on 'file', 'save as' and name your batch file e.g. 'myname' and click 'ok' (save your batch file, which has the extension *.bcf, in the same directory as the *.gjf files). 7.Click on 'exit'.

8.On the main G98W window click 'file', 'open' and navigate to the location of your .bcf file. 9.Double click on this and then click 'exit' again.

10.On the main G98W window click 'process', 'begin processing' and your batch file will start.

Note that if a calculation crashes, the process will not move on to the next job in the list automatically. By default, when an error occurs the batch file will stop completely. You can change this behavior by clicking on 'file' in the

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main G98W window, then 'preferences', 'process' and remove the check from the box ' end batch run on error'. This still does not allow the calculation to move on automatically but at least the batch file stays active and once you notice the error you can move on to the next job with a single click. For this reason it's probably best to set the order of the jobs so that the riskiest one is performed last. For instance, you may have performed optimizations on three molecules and need to run frequency calculations on them overnight, but you also have one job where you need to do both an optimization and a frequency job. The three calculations that consist of only one step should be set as the first three jobs in the batch, with the last one (which may crash and not optimize) set as the last job.

Dealing With Negative Frequencies

Use Gaussview to animate the negative frequency. Now you can see what is happening and how the atoms are moving. Very often it is a simple methyl rotation or the like. Then make a guess for where the minimum is for that imaginary frequency and optimize from there. …… 此处隐藏：2175字，全部文档内容请下载后查看。喜欢就下载吧 ……