5
$\begingroup$

I'm using GAMESS to run a geometry optimization on a thiourea molecule, using PM6. However, the output file keeps displaying the error message, "NO FORCE FIELD, SCF DOES NOT CONVERGE." Is there an error in my input code?

 $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=100 MULT=1 COORD=UNIQUE 
    NOSYM=1 $END
 $BASIS GBASIS=PM6 $END
 $DATA 
THIOUREA
C1
C          6  -0.000001   -0.216235   -0.000006
N          7  -1.149850   -0.964256   -0.062205
N          7   1.149844   -0.964254    0.062165
S         16   0.000003    1.474558   -0.000003
C          6  -2.468377   -0.327323    0.016251
C          6   2.468378   -0.327328   -0.016221
H          1  -3.255938   -1.092284   -0.077195
H          1  -2.599975    0.405207   -0.806499
H          1  -2.609097    0.216356    0.970441
H          1   3.255932   -1.092302    0.077168
H          1   2.599974    0.405143    0.806581
H          1   2.609108    0.216419   -0.970372
H          1  -1.133325   -1.963288    0.067490
H          1   1.133319   -1.963297   -0.067428
 $END
|improve this question
$\endgroup$
  • $\begingroup$ In these cases, the first thing to do might be to increase the number of SCF cycles, so try MAXIT=150, and see what happens. $\endgroup$ – Pier Jul 12 at 0:22
  • $\begingroup$ I am unfamiliar with GAMESS, but make sure you have specified the method correctly. Also, check your input geometry visually and consider switching to another method. Maybe the C-S bond is badly described in PM6. $\endgroup$ – TAR86 Jul 12 at 5:48
  • 1
    $\begingroup$ I couldn't find any indication that pm6 is actually available in GAMESS. Maybe try pm3, and see whether it works. I think pm6 would do fine for the molecule, pm3 probably too. If you require pm6 you might have to try a different ESS code. $\endgroup$ – Martin - マーチン♦ Jul 12 at 11:28
  • 1
    $\begingroup$ I spent some time yesterday trying it on WebMo (I have no local GAMESS installations on the OS I am working on right now), and even if I am not familiar with GAMESS, it looks like for some weird reason PM6 doesn't like that molecule (increased optimization and scf cycles, modified convergence criteria). If I recall correctly, anyway, it worked with PM3. $\endgroup$ – The_Vinz Jul 13 at 20:31
  • 1
    $\begingroup$ I believe the problem has to lie within GAMESS. I just ran an optimisation with Gaussian 16 B.01 and pm6, which looks like you'd would expect it. ( cc @The_Vinz ) Could you please specify the version you are using. Have you tried other molecules; did they work? Maybe good choices to localise the problem would be urea, CS2/CS, maybe the problem lies there. I'll see if I can get GAMESS to work, then I might try again. $\endgroup$ – Martin - マーチン♦ Jul 23 at 11:47
7
$\begingroup$

TL;DR: PM6 only works for elements up to fluoride in GAMESS.

I have played around with the GAMESS version installed at our cluster, the ancient 5 DEC 2014 (R1) and I came to the conclusion that there must be a 'bug' in the implementation of PM6 with GAMESS. (I reproduced the problem with 20 APR 2017 (R1); I have also downloaded 30 Jun 2019 (R1), but I won't try it as I think the result is the same.) When I tried it with Gaussian 16 Rev. B.01 on the PM6 level of theory it converged fine.

Actually, I have looked at the documentation, and it seems to be officially not supported (from INTRO.DOC):

Capabilities

   [...]
   3. Calculates semi-empirical MNDO, AM1, or PM3 models 
      using RHF, UHF, ROHF, or GVB wavefunctions.
   [...]

Or from INPUT.DOC:

        * * * semiempirical basis sets * * *

GBASIS = MNDO - selects MNDO model Hamiltonian
       = AM1  - selects AM1 model Hamiltonian
       = PM3  - selects PM3 model Hamiltonian
       = RM1  - selects RM1 model Hamiltonian
       = DFTB - selects tight binding Hamiltonian

I am pretty sure the error is associated with sulfur. I have tried a few molecules, among them $\ce{H3C-NH2}$, $\ce{(H3C)2NH}$, $\ce{(H3C)2CO}$ (see input below), urea, which converged fine. Whenever I tried a molecule containing sulfur the SCF seemed to be oscillating. I have tested $\ce{CS2}$, $\ce{SO2}$, $\ce{(H3C)2CS}$, and (obviously) thiourea. (With PM3 everything worked fine.)

My best guess is that they simply didn't finish implementing it. You could issue a support ticket on GitHub: issues. I found an article by (the here known) Jan Jensen from 2013: Project status: PM6 and PCM in GAMESS. And then from 2014: PM6, DFTB, GAMESS, enzyme design, protein-ligand binding, and protein structure validation. I stopped there.

I'd recommend using a different program, the obvious choice would be MOPAC (http://openmopac.net/). Gaussian has it implemented and a couple others probably too. Or you switch to a completely different method like xtb, HF-3c (in ORCA), DFTB (e.g. DFTB+), etc.. Depending on your system size, you can probably also get DFT based calculations done.

Here is also something related: GAMESS crash course?

 $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=100 MULT=1 COORD=UNIQUE
    NOSYM=1 $END
 $BASIS GBASIS=PM6 $END
 $DATA
 C3H6O
C1
CARBON      6.0      0.156332162        -0.059231571         0.417752882
OXYGEN      8.0      1.200569512        -0.535604279         0.831319560
CARBON      6.0     -0.037914597         1.466530485         0.340822109
HYDROGEN    1.0      0.279389785         1.860652999        -0.631337255
HYDROGEN    1.0     -1.089141584         1.742544046         0.481697509
HYDROGEN    1.0      0.545018653         1.982387227         1.112307247
CARBON      6.0     -1.053925162        -0.882111362        -0.061565447
HYDROGEN    1.0     -0.987243509        -1.102851552        -1.132983096
HYDROGEN    1.0     -1.121341433        -1.838731138         0.468944868
HYDROGEN    1.0     -1.993938204        -0.344384630         0.106761952
 $END
|improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.