CCL:G: how to freeze in gaussian

If you are trying to freeze a bond length, the simplest option would be to
 use the letter "F" after the particular bond length in the variable
 portion, say for example
 b4= x.xxx F
 Thus, that particular length will freeze during the calculation.
 But, in that case you will have to change the "Opt" keyword with
 "Popt"
 (partial optimization).
 I hope it helps.
 Regards,
 Aniruddha
 *Aniruddha Ganguly*
 *c/o Prof. Nikhil Guchhait*
 *Senior Research Fellow*
 *Department of Chemistry*
 *University of Calcutta*
 *92, A.P.C. Road*
 *Kolkata-700009*
 On Wed, Dec 16, 2015 at 5:15 AM, Sofia Vasilakaki svasilak(-)chem.uoa.gr <
 owner-chemistry=ccl.net> wrote:
 >
 > Sent to CCL by: "Sofia Vasilakaki" [svasilak%a%chem.uoa.gr]
 > Hi,
 >
 > There are a few things you might want to try. Usually 'nosymm' keyword
 > will keep the atoms fixed during opt. 'modredundant' usually works for me.
 > There are some examples here http://www.gaussian.com/g_tech/g_ur/k_opt.htm
 > (scroll down) in case you haven't seen them.
 >
 > Here http://www.ccl.net/chemistry/resources/messages/2004/06/02.007-dir/
 > is an older thread.
 >
 >
 > Cheers,
 > Sofia V.
 >
 >
 >
 > >
 > > Sent to CCL by: "kiran  k" [kd2f..mtmail.mtsu.edu]
 > > Dear CCLusers,
 > >
 > > Could anyone suggest how to find interaction energy between
 formaldehyde
 > > and
 > > fluoride ion in gaussian using z-matrix, by keeping the distance
 > constant.
 > > After the calculation, the distance changed. Here is my example input
 > look
 > > like
 > >
 ----------------------------------------------------------------------
 > > #P B3LYP/6-31+G* opt Test
 > >
 > > Geometry Optimization
 > >
 > > -1 1
 > > C
 > > O  1  r2
 > > F  1  r3  2  a3
 > > H  1  r4  2  a4  3  d4
 > > H  1  r5  2  a5  3  d5
 > > Variables:
 > > r2= 1.2246
 > > a3=  90.00
 > > r4= 1.1017
 > > a4= 122.24
 > > d4= 354.18
 > > r5= 1.1017
 > > a5= 122.24
 > > d5= 174.18
 > > constant:
 > > r3= 2.5000
 > >
 > > Thank you in advance>
 >
 >