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Alex Granovsky
gran@classic.chem.msu.su

thanks so much for your feedback.

The difference is caused by the automatically generated
H-bonds, one of the new features of DLCs in 7.1.G version.
So the entire set of DLCs is different - please take a look
at the DLC statistics.

This feature could be very useful while modeling weakly
bound systems e.g. clusters, especially when the new H-bonds
appear and old disappear during optimization process.

However, according to our observation, in some, relatively rare
cases where H-bonds are not really necessary to define a good set
of internals, adding them does can degrade the speed of geometry
optimization.

This feature is controlled by the following keyword:

  $zmat hbond=value $end

It defines the maximum possible H-bond length for the
reference O-H-O H-bond. The default is 2.1 (Angstrom).
Setting it to zero or negative value disables this feature
altogether so you can resort to the old behavior.

Best regards,
Alex

On Mon Dec 7 '09 11:17pm, Norman Shankland wrote
------------------------------------------------
>Many thanks for new Firefly release.  I was benchmarking the DLC / geometry optimization against previous results, obtained with 7.1.F.  My test case results (diltiazem cation) surprised me:
>[1] 7.1.F: equ. geom. located, NSERCH= 30, E = -1654.5411559 (CPU time = 542.5 min)
>[2] 7.1.G: equ. geom. located, NSERCH= 60, E = -1654.5411400 (CPU time = 953.0 min)

>Thus, the calculation time has effectively doubled.  The statistics on automatic coordinate generation show that the 'total number of primitives' has also doubled, from 300 (in 7.1.F) to 661 (7.1.G).

>7.1.G claims an improved DLC engine - are longer compute times a consequence of these improvements?

>Thanks in advance,

>Norman

>Note: test case input as follows, running under Windows XP / Intel Core 2 Quad :
>$CONTRL RUNTYP=OPTIMIZE COORD=ZMTMPC ICHARG=1 MAXIT=1000 NPRINT=-5 NZVAR=1 $END
>$ZMAT DLC=.T. AUTO=.T. $END                                                    
>$SYSTEM TIMLIM=1440 MWORDS=200 $END                                            
>$SCF DIRSCF=.T. $END                                                          
>$P2P P2P=.T. DLB=.T. MXBUF=2048 $END                                                    
>$STATPT NSTEP=1000 NPRT = -2 $END                                              
>$BASIS GBASIS=N31 NGAUSS=6 NPFUNC=1 NDFUNC=1 $END                              
>$GUESS GUESS=HUCKEL KDIAG=0 $END                                              
>$ELMOM IEMOM=0 $END                                                            
>$DATA
>