Convergence issues with DFT

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Hello everyone,

I'm having some problems while modeling a Au cluster embedded with organic molecules using DFT. I divided my system in fragments and they converge normally, except for the geometry with the gold atoms. The calculation crashes after few minutes, with this error message:

 Caching 1-el integrals 
Rotation of axis
Time after variat. SCF: 10.1
Time prior to 1st pass: 10.1

     Calculation failed to converge
------------------------------



        Total DFT energy =    -1266.929870285030
One electron energy = -6933.564657988991
Coulomb energy = 3495.147445437451
Exchange-Corr. energy = -132.476286200324
Nuclear repulsion energy = 2303.963628466834

Numeric. integr. density =      189.363633890303

    Total iterative time =    178.8s



                 Occupations of the irreducible representations
----------------------------------------------

                    irrep           alpha         beta
-------- -------- --------
a 32.0 32.0
e+ 63.0 63.0
e- 0.0 0.0

------------------------------------------------------------------------
dft energy failed 0
------------------------------------------------------------------------
This type of error is most commonly associated with calculations not reaching convergence criteria
------------------------------------------------------------------------




The relevant parts of my code are:
geometry gold_atoms units angstroms print xyz
Au 6.12310 4.84578 -5.53734
Au 7.51336 3.65903 -3.10756
Au 4.85023 3.53199 -1.64584
Au 7.20854 4.97958 -0.38574
Au 5.81829 6.16632 -2.81553
Au 4.42805 7.35307 -5.24530
Au 3.45997 4.71874 -4.07563
Au 3.15516 6.03928 -1.35381
Au 5.51348 7.48686 -0.09372
Au 4.12323 8.67361 -2.52350
end

basis spherical
 Au library SBKJC_VDZ_ECP
end

ECP ### SBKJC_VDZ_ECP basis set library
Au nelec 60
Au ul
1 4.3876300 -10.7235800
Au S
0 1.5563600 6.3561200
2 3.7159300 -364.4403900
2 4.0679200 428.1975300
Au P
0 1.1879800 4.4151800
2 3.0155100 -136.5755000
2 3.5958800 194.2053500
Au D
0 35.2500000 8.8819800
2 5.0230700 86.7661200
Au F
0 1.6888100 6.2160300
END

set geometry gold_atoms
dft
xc pbe0
grid fine
print low
vectors input atomic output gold_atoms.mo
end
task dft energy

Do anyone have some advice of what am I doing wrong? I've tried changing the grid, the xc function, the basis set, but none of these works. About the geometry, it is a cut from a Au55 cuboctahedron, so I would like to keep it that way. Any hints?

  • Huub Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Hi Moretto,

The problem with your calculation is summarized in the following warning message in the output:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

if you add "symmetry c1" to your geometry to turn the use of symmetry off you will find the calculation converges no problem.

Best wishes, Huub

Just Got Here
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Quote:Huub Jul 2nd 6:08 pm
Hi Moretto,

if you add "symmetry c1" to your geometry to turn the use of symmetry off you will find the calculation converges no problem.

Best wishes, Huub


It worked! Thank you very much!


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