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Alex Granovsky
gran@classic.chem.msu.su

 $STATPT OPTTOL=0.0001 NSTEP=20 Method=CONOPT $END
 $STATPT IFREEZE(1)=15,10,20,16 $END

Formally, your input direct Firefly to freeze the following cartesian coordinates:

Z coordinate of atom # 5,
X coordinate of atom # 4,
Y coordinate of atom # 7, and
X coordinate of atom # 6

However, the ifreeze array is simply ignored during Method=CONOPT runs
(although I'm not completely sure whether this is properly documented, or not).

Method=CONOPT is considered as the obsolete feature and it is
generally not recommended to use it.  

Thus, you either need to switch to any other available method of geometry optimization (provided you specify your ifreez array correctly), or (as Pedro already suggested) to use DLCs.

You may find the following threads on forum of some help to you:

http://classic.chem.msu.su/cgi-bin/ceilidh.exe/gran/gamess/forum/?C33a475164csW-6284-323-00.htm

http://classic.chem.msu.su/cgi-bin/ceilidh.exe/gran/gamess/forum/?C357c265d24el-6758-1036-00.htm

http://classic.chem.msu.su/cgi-bin/ceilidh.exe/gran/gamess/forum/?C3d4763b0bbHW-6057-1205+00.htm

Regards,
Alex Granovsky




















On Tue Feb 3 '09 8:22pm, jaber jahannbin Sardroodi wrote
--------------------------------------------------------
>Dear Alex,

>Thank you for your kindly consideration. Please here is the input file for tetracene geometry optimization with restrictions on end-to-end distance.

>thank you again,
>
>
>
>On Wed Jan 28 '09 9:19pm, jaber jahannbin Sardroodi wrote
>---------------------------------------------------------
>>Dear PcGamess experts,
>>Hi,
>>I need to optimize a curved structure of tetracene. I use RHF and B3LYP level of DFT. In order to maintaining the curvature of structure, I set end-to-end distance restricted using IFREEZE(1). However, the computations never get a minimum in enegry and are divergence. I think this is due to the structure's instability (when the end-to-end distance restriction is removed, the computations become convergence). Please kindly write me what method is appropriate for optimizing such high energy sructures.
>>Sincerely yours,
>>Jaber