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Re: SCF unstable from beginning in ma-def2-TZVP basis.

olgerdovich
olgerdovich@yandex.ru

Your molecule is a large flat aromatic one, and it is very likely reason to induce severe linear dependence in large basis with diffuse functions. Indeed, your have this caution in your out-file:

                  * * * WARNING * * *
------------------------------------------------------------------------------
THE OVERLAP MATRIX HAS  124 EIGENVALUES BELOW 1.1E-03.
THE SMALLEST OF THESE IS 3.15022E-09.
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).

EIGENVALUES BELOW 1.0D-07 PROBABLY WON'T CONVERGE.
EIGENVALUES BETWEEN 1.0D-07 AND 1.0D-06 MAY REQUIRE
TIGHTENING OF -NCONV- DENSITY CONVERGENCE IN $SCF.


and you have THE SMALLEST value OF 3.15022E-09, which is 30 times less than "EIGENVALUES BELOW 1.0D-07 PROBABLY WON'T CONVERGE".

It appears to me that you have to exclude some basis functions manually (indicated in the warning in your output, most likely they are diffuse functions of atoms in the middle of your molecule), and this question has been discussed here in details, use the keyword "linear dependence" to search. If you study a series of similar compounds, you should do it in a consistent way, to make it so that in a series of compounds examined by QC method the problematic basis functions are removed uniformly and do not induce errors due to different basis sets.





On Sat Feb 3 '18 2:14am, Ian Dunn wrote
---------------------------------------
>I have been running DFT calculations successfully on a chromophore molecule (perylene diimide) in the DZV, def2-SVP, and ma-def2-SVP basis sets. However, when I attempt to run the calculation in the ma-def2-TZVP basis set, the SCF cycles look horrible from the beginning, as seen in the output snippet below.  I take the ma-def2-SVP and ma-def2-TZVP basis sets from https://comp.chem.umn.edu/basissets/basis.cgi from which I translate the Gaussian basis set files into GAMESS US format myself. I've attached the Firefly output file (including the input) with the basis set definition added to the end of the file.  Any thoughts on why this calculation is behaving so poorly?  Thanks in advance!!!

> ITER EX DEM  TOTAL ENERGY      E CHANGE  DENSITY CHANGE    DIIS ERROR^M
>   1  0  0 -1324.981240495 -1324.981240495************** 541.060596764^M
>   2  1  0  -722.443909720   602.537330775************** 768.416928805^M
>   3  2  0  -952.956399533  -230.512489813************** 710.176294049^M
>   4  3  0  -948.584694079     4.3717054546580.221911676 723.293180098^M
>   5  4  0  -978.842533897   -30.2578398185802.546052429 709.124323785^M
>   6  5  0  -938.586590377    40.2559435204056.628384960 732.599576927^M
>   7  6  0  -988.084298958   -49.4977085823469.581436544 702.543642671^M
>   8  7  0  -940.327360467    47.7569384912940.712600840 780.888972782^M
>   9  8  0  -979.792346209   -39.4649857422524.864474960 741.559270005^M
>  10  9  0  -980.144126287    -0.351780078************** 729.249202499^M
>  11 10  0  -955.575882962    24.5682433256237.998460740 742.574178267^M
>  12 11  0  -952.486151551     3.0897314113010.996780641 756.693942400^M

>

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