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Trouble with G98 PCM caculations, "Increase the MxTs"?

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Member
Registered: Apr 2009
Posts: 3
Hello, everyone
I've got an undergraduate struggling with a fairly ambitious computational project for his senior thesis, trying to model some transformations of nicotine in water solutions. He's running with the PCM model in B3LYP/6-31G**, and has a recurring problem that I can't find anywhere in the Gaussian manual. Unfortunately, all of my expertise is in gas phase calculations, and I'm at a loss. It's also frustrating, because a quick search of the CCL archives shows that this problem shows up annually... but there are no posted solutions! So I've come here instead in hopes of finding help.

The problem begins when the PCM calculation fails due to insufficient tesserae. We use TSNUM to increase that value, and the job will often converge. However, in some recent cases with the larger basis set, we run into an error that we can't explain. A sample:

Solvent: WATER
Model : PCM/UAHF, Icomp = 2
Version: MATRIX INVERSION
Cavity : ICOSAHEDRA with 320 initial tesserae
------------------------------------------------------------------------------
Nord Group Hybr Charge Alpha Radius Bonded to
1 CH sp2 0.08 1.20 1.815 C2 [s] N6 [d]
2 C sp3 0.08 1.20 1.500 C1 [s] C3 [s] C11 [s]
3 CH sp2 0.08 1.20 1.905 C2 [s] C4 [d]
4 CH sp2 0.08 1.20 1.815 C3 [d] C5 [s]
5 CH sp3 0.08 1.20 1.635 C4 [s] N6 [s]
6 N sp2 0.08 1.20 1.590 C1 [d] C5 [s]
11 CH sp3 0.08 1.20 1.680 C2 [s] C13 [s]
13 CH2 sp3 0.08 1.20 1.860 C11 [s] C16 [s]
16 CH2 sp3 0.08 1.20 1.680 C13 [s] C19 [s]
19 CH2 sp3 0.08 1.20 1.770 C16 [s] N22 [s]
22 NH sp3 0.08 1.20 1.590 C19 [s] C24 [s]
24 CH3 sp3 0.08 1.20 1.860 N22 [s]
------------------------------------------------------------------------------
Too many tesserae. Increase the MxTs.
Error termination via Lnk1e in c:\program files\g98w\l502.exe.

I do not know HOW to increase the MxTs, nor what a reasonable number might be. (This job was run with TSNUM=300) We would both very much appreciate any input!

Thanks in advance.
Member
Registered: Sep 2007
Posts: 20
I have no idea about this stuff, but just based on pattern recognition and guessing, MxTs sounds like Maximum Tesserae (whatever that is :)), which in turn sounds like what you are already doing with TSNUM. So, perhaps you can try increasing the number even more. Anyway, just felt like replying to a topic I know nothing about :)
Did you check this error with the developers?
Member
Registered: Apr 2009
Posts: 3
Thanks for the quick reply. I don't know if it's quite that easy. We only added the TSNUM command in order to avoid this same error having cropped up with a smaller number. It seems that no matter what we pick for TSNUM, we manage to generate ever-so-slightly more tesserae than that number. But, for lack of better ideas, we'll keep cranking up the TSNUM.

I haven't ever checked an error with the developers... how exactly does one do that?
Member
Registered: Sep 2007
Posts: 20
I think they have some e-mail like help@blabla, but I don't know if it is really intended for user questions. I'm sure it's on their web site, maybe you can have a look.
Member
Registered: Apr 2009
Posts: 3
Just to get the message out there... I DID get a response from the Gaussian help address, and it was ... well, pointed:


Dr. Dransfield,

Thank you for giving us a chance to comment. The short answer here is
that you are out of luck. G98W had fixed arrays for holding the tiles
for the solvent cavities. These could not be changed at run time and you comment that you are trying to increase TSNum to get good results. This is a collision course.

We completely rewrote this code for Gaussian03 and have improved it further for Gaussian 09. There is no option for changing G98W. You can try decreasing the number of tiles but that probably has other drawbacks.

Do you have access to Gaussian03? Possibly with a colleague at another university who could run a calculation for you?

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