Summary: G98: VOVl3 problem: convergence criterion not met

 Hello,
 here is the summary of all the answers I got for my problem. Thanks (in
 alphabetically order) to Laurence Cuffe, Kerwin Dobbs, Paul Kiprof, Liviu
 Mirica, Cory Pye and Dave Shobe.
 The problem was solved by increasing the number of SCF cycles, as
 suggested by many. This seems very often necessary with transition metals.
 The two other suggestions (using first a small basis set before switching
 to the larger, or turning off "vshift", did not work, unfortunately.
 Thanks again,
 R.Herrmann.
 The original question:
 ----------------------------------------------------------------------------
 Hello,
 I recently tried to calculate the NMR chemical shifts of VOCl3
 with Gaussian 98:
 ---------------------
 #B3LYP/6-31G* SP NMR
 VOCl3
 0 1
 cl
 cl   1 clcl2
 cl   2 clcl3      1 clclcl3
  o   3 ocl4       2 oclcl4       1 dih4
  v   3 vcl5       2 vclcl5       1 dih5
 clcl3       3.506243
 clclcl3      59.999
 ocl4        2.938735
 oclcl4       53.376
 dih4        -64.586
 vcl5        2.118170
 vclcl5       34.144
 dih5        -31.640
 -----------------------
 The result (even with several variations in the input) is always an
 error termination when trying the "incremental Fock formation"
 (convergence criterion not met). The structure was optimized with
 GAMESS.
 Any suggestion what I could do is wellcome - thank you!
 ------------------------------
    108 basis functions      288 primitive gaussians
     41 alpha electrons       41 beta electrons
        nuclear repulsion energy       561.9817715949 Hartrees.
  One-electron integrals computed using PRISM.
  NBasis=   108 RedAO= T  NBF=   108
  NBsUse=   108 1.00D-04 NBFU=   108
  Projected Huckel Guess.
  Requested convergence on RMS density matrix=1.00D-08 within  64 cycles.
  Requested convergence on MAX density matrix=1.00D-06.
  Virtual orbitals will be shifted by   0.200 hartree.
  Restarting incremental Fock formation.
  Restarting incremental Fock formation.
  Restarting incremental Fock formation.
  >>>>>>>>>> Convergence criterion not met.
  SCF Done:  E(RB+HF-LYP) =  -2359.59549049     A.U. after   65 cycles
              Convg  =    0.5851D-03             -V/T =  1.9657
              S**2   =   0.0000
  Convergence failure -- run terminated.
  Error termination via Lnk1e in /usr/local/g98_a7/l502.exe.
  Job cpu time:  0 days  0 hours 16 minutes 33.0 seconds.
  File lengths (MBytes):  RWF=   14 Int=    0 D2E=    0 Chk=    1 Scr=    1
 --------------------------------------------------------------------------
 The answers:
 1. From: Kerwin D Dobbs <Kerwin.D.Dobbs-: at :-USA.dupont.com>
 To: "Rudolf Herrmann <herrmann" <herrmann-: at :-itqb.unl.pt>
 Subject: Re: CCL:G98: VOCl3 problem: convergence criterion not met
 Dr. Herrmann,
 Try turning off the "vshift" by changing the line,
 #B3LYP/6-31G* SP NMR
 to
 # B3LYP/6-31G* SP NMR IOP(5/10=-1)
 When there is a TM in the molecule, G98 automatically turns
 on "VSHIFT" which usually makes SCF convergence worse. The
 above addition to your line turns off "VSHIFT". Give it a try and
 see what happens.
 Kerwin
 ------------------------------------------------------------------
 2. From: Cory Pye <cpye-: at :-crux.stmarys.ca>
 To: Rudolf Herrmann <herrmann-: at :-itqb.unl.pt>
 Subject: Re: CCL:G98: VOCl3 problem: convergence criterion not met
 Hello,
 your SCF is not converging. Try running, at first, HF/STO-3G. If it works,
 then
 Then try B3LYP/6-31G* afterwards with guess=read in the input. It usually
 works like a charm for me, I always use something like this.
 -Cory
 ----------------------------------------------------------------------
 3. From: Liviu Mihail Mirica <liviu-: at :-Stanford.EDU>
 To: Rudolf Herrmann <herrmann-: at :-itqb.unl.pt>
 Subject: Re: CCL:G98: VOCl3 problem: convergence criterion not met
 Try adding SCFcyc=1000 in your command lines. This will increase the # of
 SCF cycles up to the desired number (1000 in this case). that should be
 enough for your system.
 ------------------------------------------------------------------------
 4. From: Laurence Cuffe <Laurence.Cuffe-: at :-ucd.ie>
 To: Rudolf Herrmann <herrmann-: at :-itqb.unl.pt>
 Subject: Re: CCL:G98: VOCl3 problem: convergence criterion not met
 And it should run these keywords change the default SCF method
 and then increase the number of SCF cycles allowed.  I got the job
 to complete in about 50 minutes running it in core on a linux box
 with a memory limit of 600MB but it this doesn't make sense to
 you don't worry about it. Try using the modified line above and if
 there are any problems don't hesitate to come back to me.
 All the best
 Laurence Cuffe
 -------------------------------------------------------------------------
 5. From: Paul Kiprof <pkiprof-: at :-d.umn.edu>
 To: herrmann-: at :-itqb.unl.pt
 Subject: VOCL3
 Dear Dr. Herrmann,
 I would add to the input
 SCF(direct,qc,maxcycle=1000)
 This will increase the number of convergence cycles and hopefully converge
 the calculation. I always do that when I have transition metal compounds.
 Best wishes,
 Paul Kiprof
 ---------------------------------------------------------------------------
 6. From: "Shobe, Dave" <dshobe-: at :-sud-chemieinc.com>
 To: 'Rudolf Herrmann' <herrmann-: at :-itqb.unl.pt>
 Subject: RE: G98: VOCl3 problem: convergence criterion not met
 The standard 64 SCF "cycles" (or iterations of the variational
 procedure)
 is
 rarely enough for transition metal compounds, even closed shell ones like
 VOCl3.  Read the section in the Gaussian manual describing the "scf"
 keyword, and you will find various options which may improve the
 convergence.  A lot of it is trial and error, with these different scf
 options.  The simplest is scf(maxcyc=999) which increases the number of
 cycles/iterations to 999 before the program "gives up" and prints the
 error
 message.  Scf=qc and scf(vshift=###) have also been useful in my
 experience.
 More advice: once you get a good wavefunction, make a backup of the
 checkpoint file, so if the wave function becomes corrupted in subsequent
 calculations you can always go back to it.
 ----------------------------------------------------------------------------
 --
 Dr. Rudolf Herrmann
 Instituto de Tecnologia Quimica e Biologica (ITQB)
 Av. da Republica, EAN,  Apt. 127
 P-2781-901 Oeiras
 e-mail: herrmann-: at :-itqb.unl.pt