Re: [AMBER] unable to find mopac charges

From: Anselm Horn <>
Date: Mon, 15 Oct 2012 09:07:38 +0200

Am 11.10.2012 14:00, schrieb David A Case:
> On Thu, Oct 11, 2012, Anogna wrote:
>> I am not able get whats the problem. Can you plz help with this.
> The mopac job never completed, and did not show any error messages in the file
> itself. I suggest running the mopac job by hand, to see if any messages come
> to stderr. A reason for moving from mopac to our own code (sqm) is so that we
> would have a chance to debug problems that arise. Given that the current
> codes work, I doubt that anyone on the list will have enough knowledge of
> mopac internals to be able to help here. My only WAG is to check that your
> job didn't run into some local time or disk limit that forced it to quit.

The Mopac job most probably aborted because the wave function optimizer
was not able to find a stable wave function for the system within the
given number of steps.

In a QM geometry optimization (as in this example) you minimize the
total energy with respect to the atom coordinates; however, for each new
structure (= set of atom coordinates) you have to find a correct wave
function, i.e. distribute the electrons into the molecular orbitals and
change their shape, so that the electronic energy is at a minimum.

Thus, such an QM optimization is a double loop of minimizations and each
has its own maximum number of steps.

In old versions of Mopac and similar programs a failure of the wave
function optimization was not explicitely stated in the out file; the
user had to guess the reason of program abort from the output message
meaning that Mopac applies all measures it has to find a stable wave
function (but obviously failed).

In this case the wave function for the initial structure could not be
built up, which may also be a hint for a bad input structure or wrong
electronic configuration.

After that explanation, a more practical hint:
The number of wave function iteration steps is set by the keyword
ITRY=NNN, where NNN defaults to 200 or so. One could try to increase
this by explicitely setting ITRY=999 or even use larger values.

However, I never ran Mopac from within antechamber, so I do not know the
exact syntax for adding extra keywords to the Mopac keyword line (the
first in the input file containing the keyword AM1).



Institut für Biochemie
Friedrich-Alexander-Universität Erlangen-Nürnberg

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Received on Mon Oct 15 2012 - 00:30:26 PDT
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