I am trying to calculate the inversion angle interaction among four connected atoms but I found that almost no inversion is calculated for many forcefield such as cvff, pcff and COMPASS even if I have defined the inversion explicitly in the potential function. note that geometrially, there is an inversion among four connected atoms. Very few inversions can be recognized by MS and calculted. I check the help document and found that MS defined inversion following some mechanism which is not shown clearly. anyone konw how to defined an inversion angle in MS so that such inversion can be recognized by MS?