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Thomas Pijper
thomaspijper@hotmail.com

When I run the two input files you provide, I get the following results (with the 6-31G(d) basis):

trans: -276.9221211
gauche: -276.9214031

This is an exact match with the results by Wiberg et al (note their paper is published in J Phys Chem, not J Am Chem Soc). As such, I'm not able to reproduce your problem.

Can you provide a few more details, such as what results you get?

BTW, if you see a mismatch between calculated and published results with the 6-311G basis, this could be due to the absence of the D5 keyword in $CONTRL. For the 6-311G basis, D5 should be set as .T. (default is .F.). For more information, see the chapter on basis sets in the Firefly manual.


Kind regards,
Thom





On Tue Dec 9 '14 7:28pm, Mark Edgar wrote
-----------------------------------------
>Dear Firefly users,

>I have used Gaussian-03 to calculate the optimised structures and enegry difference between the trans and gauche rotamers of 1,2-difluoro-ethane using RHF and a variety of basis sets. My results match the data published in the paper by Wiberg etal Journal Americal Chemical Society, Vol 94, No 18, p6956, (1990) , where the favoured rotamer is the trans form for "simple" basis sets and the gauche form for "complex" basis sets. Experimental results show that the gauche form is lowest in energy.

>Calculating the same gauche/trans structures and energies using Firefly have produced rather different results (I am still learning and trust that there is an error in my Firefly input file).

>All help and guidance will be welcome.
>Thanks in advance to anyone that can help.

>Regards,

>Mark
>
>
>
>INPUT DATA FILES (trans and gaughe)

>!                        
>! F-CH2-CH2-F Trans
>!                  
> $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=900 COORD=ZMT nprint=-9 $END
> $CONTRL ICUT=11 INTTYP=HONDO $END
> $SYSTEM TIMLIM=600 MEMORY=9900000 SPLITF=.T. $END
> $statpt nstep=900 $END
> $p2p p2p=.t. dlb=.t. XDLB=.T. $END
> $SMP CSMTX=.T. $END
> $SCF    DIRSCF=.True.  NCONV=6 $END              
> $GUESS  GUESS=HUCKEL   $END        
> $BASIS  GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=0 $END              
> $ELMOM  IEMOM=2 WHERE=COMASS $END        
> $DATA    
>RHF/6-31G* F-CH2-CH2-F Trans  
>CN 1  

>F
>C  1   B1  
>C  2   B2    1    A1  
>F  3   B1    2    A1    1   180.0
>H  2   B3    1    A2    3   D1
>H  2   B3    1    A2    3   -D1  
>H  3   B3    4    A2    2   D1
>H  3   B3    4    A2    2   -D1

>B1 1.4
>B2 1.51
>B3 1.07
>A1 107.0
>A2 109.5
>D1 119.9
> $END
>
>
>
>
>!                        
>! F-CH2-CH2-F Gauche
>!                  
> $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=900 COORD=ZMT nprint=-9 $END
> $CONTRL ICUT=11 INTTYP=HONDO $END
> $SYSTEM TIMLIM=600 MEMORY=9900000 SPLITF=.T. $END
> $statpt nstep=900 $END
> $p2p p2p=.t. dlb=.t. XDLB=.T. $END
> $SMP CSMTX=.T. $END
> $SCF    DIRSCF=.True.  NCONV=6 $END              
> $GUESS  GUESS=HUCKEL   $END        
> $BASIS  GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=0 $END              
> $ELMOM  IEMOM=2 WHERE=COMASS $END        
> $DATA    
>RHF/6-31G* F-CH2-CH2-F Gauche  
>CN 1  

> F
> C    1    B1
> C    2    B2    1    A1
> F    3    B1    2    A1    1    D3
> H    2    B3    3    A2    4   -D1
> H    3    B3    2    A2    1   -D1
> H    2    B4    3    A3    4   D2
> H    3    B4    2    A3    1   D2

>B1  1.5
>B2  1.5
>B3  1.07
>B4  1.07
>A1  109.0
>A2  109.0
>A3  109.0
>D1  60.0
>D2  180.0
>D3 70.0
> $END

>