Many thanks, David<br>I did the frequency calculation, and i got the bending force constant(0.2331) and the stretch force constant(0.8402). but I can't associate them to the force constant in the opls FF. and as a test,i also calculate the stretch force constant of H-C(2.4214) and C-C (6.1634), the value is not proportional to the value in opls ff (C-C:224412.5 C-H:284702.4). can you give some more advice, thank you again.<br><br>the frequency calculation output as follow<br> <br>C-C<br> ?A <br>Frequencies -- 1063.9177<br>Red. masses -- 3.6307<br>Frc consts -- 2.4214<br>IR Inten -- 0.0000<br>Raman Activ -- 16.1188<br>Depolar -- 0.2891<br><br>C-H<br>Frequencies -- 3182.0979<br>Red. masses -- 1.0331<br>Frc consts -- 6.1634<br>IR Inten -- 72.1900<br>Raman Activ -- 0.0000<br>Depolar -- 0.0302<br><br>I-I-I(bending)<br> 1 <br> PIU <br> Frequencies -- 55.8400 <br> Red. masses -- 126.9004 <br> Frc consts -- 0.2331 <br> IR Inten -- 0.0874 <br><br>I-I-I(stretch )<br> 3 <br> Frequencies -- 106.0065<br> Red. masses -- 126.9004<br> Frc consts -- 0.8402 <br>IR Inten -- 0.0000<br><br> <br><br><br><br>> On Sat, 2005-04-16 at 11:11 +0800, zjim wrote:<br><br>> > hi every one<br><br>> > when there is no parameter for some atom types of a molecule, such as<br><br>> > triiodide ion . Quantum mechanics calculation method (DFT MP2) seems<br><br>> > to a reasonable solution. the partial charge is easy to calculate by<br><br>> > add the key words "ChelpG", but how to calculate the force constant<br><br>> > (fc) of the bond , angle ,together with dihedral. If there is someone<br><br>> > know, please give some advice. <br><br>> > thank you very much!<br><br>> In principle you can deduce it from a frequency calculation.<br><br>> <br><br>> > <br><br>> > Zhou Jin ming<br><br>> > Shanghai Institute of Organic Chemistry<br><br>> > Computational Chemistry Lab<br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > 什么邮箱可以设置 图片签名档,发送电子名片? <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > <br><br>> > 什么邮箱可以设置 图片签名档,发送电子名片? <br><br>> > <br><br>> > _______________________________________________<br><br>> > gmx-users mailing list<br><br>> > gmx-users@gromacs.org<br><br>> > http://www.gromacs.org/mailman/listinfo/gmx-users<br><br>> > Please don't post (un)subscribe requests to the list. Use the <br><br>> > www interface or send it to gmx-users-request@gromacs.org.<br><br>> -- <br><br>> David.<br><br>> ________________________________________________________________________<br><br>> David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,<br><br>> Dept. of Cell and Molecular Biology, Uppsala University.<br><br>> Husargatan 3, Box 596, 75124 Uppsala, Sweden<br><br>> phone: 46 18 471 4205 fax: 46 18 511 755<br><br>> spoel@xray.bmc.uu.se spoel@gromacs.org http://xray.bmc.uu.se/~spoel<br><br>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<br><br>> <br><br>> _______________________________________________<br><br>> gmx-users mailing list<br><br>> gmx-users@gromacs.org<br><br>> http://www.gromacs.org/mailman/listinfo/gmx-users<br><br>> Please don't post (un)subscribe requests to the list. Use the <br><br>> www interface or send it to gmx-users-request@gromacs.org.<br><br>> <br><!-- footer --><br>