Symmetry fudging and degeneracy


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Forum Vet
2:29:56 PM PST - Fri, Nov 11th 2011
It seems that the initial guess does not give you the best choice of orbitals using the atomic guess. A couple of approaches could work:

1. Easiest is to try "vectors input hcore" in the dft block, which might give you slightly different orbitals that help the minimizer find its path.

2. Run SCF for like 20-30 iterations (Use "scf ignore" so that the calculation is sure to continue) and use those vectors as an input for the DFT.

Bert


Quote: Nov 9th 12:37 am
I have been trying to run DFT calculations on partially fluorinated vanadyl napthalocyanine (527 electrons) and unfluorinated vanadyl phthalocyanine (295 electrons) (both C4v symmetry, enforced) using simple basis sets (3-21g or 6-31g) and B3LYP as an exchange functional. While my jobs are successful, all of the outputs have included "symmetry fudging" and warnings about the HOMO and LUMO being degenerate. Some of the jobs barely reach convergence after 120 iterations. What can I do to improve my calculations? I am already using simple basis sets, so should I switch to HF instead of DFT? Here is one of my VONc-F16 input file without the coordinates:

start voncfjob9

ECHO
ECCE_PRINT /dtemp/bock788/VONcF/VONcFjob9/eccejob9.out

charge 0
geometry units angstroms
[coordinates here]
symmetry c4v print
end


basis spherical
  • library 6-31g
end

dft
mult 2
iterations 120
xc b3lyp
end


driver
maxiter 60
end

task dft energy

And here are some of the common warning messages in my output files:

Warning: spatial symmetry breaking in UKS: alpha =  2.15E-02

d= 0,ls=0.0,diis     2  -4860.6199036872  2.46E+01  5.32E-03  4.58E+01    21.7



Symmetry fudging

Warning: spatial symmetry breaking in UKS: alpha =  3.09E-02

d= 0,ls=0.5,diis    47  -4887.6388975884 -1.53E-06  1.64E-06  5.28E-06   189.5

                                                    4.72E-07  5.19E-06
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Warning - the HOMO and LUMO are degenerate and you are using symmetry.

This can lead to non-variational energies and poor convergence.

Modify the initial guess, or use an open-shell wavefunction, or turn

off symmetry.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks in advance, any help is greatly appreciated.