Subject: semi-empirical calculations....

From: Stevie T <[email-masked]>
Date: Wed, 06 May 1998 11:31:10 +0100

Hi all...

I have recently been doing some dipole moment calculations using the AM1

and PM3 semi-empirical methods in Hyperchem. I have been trying the
caculations at different torsion angles and obtaining some reasonable
results. However, occasionally a difference as small as 10 degrees makes

the dipole moment value increase from 4D to about 4000D. Has anyone else

had this problem ? What do people think of the accuracy of
semi-empirical calculations for such properties as dipole moments ?

Also, when the calculations were repeated under Mopac/AM1 and Mopac/PM3
in Cerius2 they yielded reasonable results. I presume this is to do with
the individual ways in which the two similar methods are implemented
under different packages (ie Hyperchem and Mopac). Has anyone any ideas
on this or any references to work done on this ?

Cheers in advance... and I'll summarise...

Steve Todd

--

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