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Re: Perfluorinated carboxylic acid geo opt fails with no indication why.

Alex Granovsky
gran@classic.chem.msu.su


Hi Gordon,

Actually, you have the error message at the end of output:

SCF DID NOT CONVERGE...NO MPLEVL=2 CALCULATION

There is a partial linear dependence in your basis set that negatively
affects convergence. There is also the corresponding warning in the output:

THE OVERLAP MATRIX HAS    4 EIGENVALUES BELOW 1.0E-05.
THE SMALLEST OF THESE IS 2.63936E-06.
THIS INDICATES A PARTIAL LINEAR DEPENDENCE IN YOUR ATOMIC BASIS.

TO OBTAIN SCF CONVERGENCE MAY REQUIRE
MORE ACCURATE INTEGRAL EVALUATION (INTTYP=HONDO, ICUT=11, ITOL=30 IN $CONTRL),
MORE ACCURATE DIRECT SCF FOCK MATRIX FORMATION (FDIFF=.FALSE. IN $SCF), OR
CHANGING CONVERGERS (DIIS=.T. SOSCF=.F. IN $SCF).

Note, 6-311 is a spherical basis set, so some part of this dependence
may be because of missed d5=.t. keyword. Next, you do not actually
need diffuse functions on carbons, so you may add proper elneg
directive to improve convergence. Finally, to get reasonable
precision with MP2, you actually need to tighten nconv for all
calculations with partial linear dependence; see the documentation
on the MP2 code.

regards,
Alex Granovsky


On Tue Sep 7 '10 2:56pm, Gordon wrote
-------------------------------------
>Dear forum followers,

>I have a compound CF3(CF2)7CH2COOH which I am having problems with in terms of geometry optimisation.  I am using MP2 6-311+G(d,p) level of theory, and am correcting with vibrational frequencies.  For some reason, this run always stops, without any other indication than "EXECUTION OF FIREFLY TERMINATED ABNORMALLY...".

>I initially optimse the "hand drawn" structure using a forcefield (MMFF94, 100 iterations, steepest decent etc) in Avogadro, export as an .xyz file, and import to GabEdit to construct the input file.  I have tried changing the optTol = 1 E-5 to optTol = 5 E-4 without any improvement.  This is a typical method for me, and in general I do not encounter problems, and definitely never like this.

>I've attached the .inp and .out files here, in case anyone might have some insight as to why this problem is occurring.

>Cheers,
>Gordon


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