Wrong ordering of energy levels

From NWChem

Viewed 2510 times, With a total of 2 Posts
Jump to: navigation, search

Clicked A Few Times
Threads 5
Posts 21
Hi,

I noticed that sometimes converged DFT calculations give the Kohn-Sham orbitals (which are printed right after the converged energy) in a funny order. Around the Fermi energy, the orbitals are not ordered with increasing energy such that some orbitals are said to be occupied when in fact they shouldn't be. For example :

Vector  835  Occ=2.000000D+00  E=-1.725603D-01
MO Center= 4.1D-01, 7.7D-01, 1.2D+00, r^2= 3.1D+01
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
2155 0.290222 203 Pd dyz 1697 -0.287172 184 Pd dxz
1435 -0.285856 173 Pd dyz 2225 0.280435 206 Pd dxz
1721 -0.259931 185 Pd dxz 2177 0.241332 204 Pd dxz
1745 -0.234405 186 Pd dxz 1673 -0.232804 183 Pd dxz
2035 0.220113 198 Pd dyz 2032 -0.213596 198 Pd dxy

Vector  836  Occ=2.000000D+00  E=-1.708588D-01
MO Center= 1.0D+00, -4.2D-01, 1.1D+00, r^2= 3.1D+01
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
1502 -0.206055 176 Pd pz 1915 0.198638 193 Pd dyz
1645 0.194995 182 Pd py 1315 -0.191369 168 Pd dyz
1193 0.186496 163 Pd dxz 1888 0.174989 192 Pd dxy
1478 0.166567 175 Pd pz 2297 -0.160579 209 Pd dxz
1455 -0.158688 174 Pd dxx 1699 -0.158116 184 Pd dyz

Vector  837  Occ=0.000000D+00  E=-1.737251D-01
MO Center= 1.2D+00, -2.3D-01, 9.2D-01, r^2= 2.7D+01
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
2032 -0.243681 198 Pd dxy 1384 0.239949 171 Pd dxy
1336 -0.235336 169 Pd dxy 1624 -0.229898 181 Pd dxy
1192 0.195941 163 Pd dxy 1460 -0.178903 174 Pd dzz
2176 0.178709 204 Pd dxy 1241 0.178167 165 Pd dxz
1408 -0.177786 172 Pd dxy 1506 -0.171399 176 Pd dyy

Vector  838  Occ=0.000000D+00  E=-1.722297D-01
MO Center= 8.4D-01, -9.0D-01, 1.1D+00, r^2= 2.8D+01
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
1433 0.224043 173 Pd dxz 1792 -0.204859 188 Pd dxy
1264 0.199807 166 Pd dxy 1432 -0.196589 173 Pd dxy
1673 -0.180613 183 Pd dxz 1480 0.174413 175 Pd dxy
1555 -0.169257 178 Pd dyz 2177 0.166209 204 Pd dxz
1815 -0.158712 189 Pd dxx 1697 -0.156071 184 Pd dxz

Is there a reason for this? Couldn't this affect other values calculated from the converged density since it comprises orbitals that shouldn't be occupied in reality?

Thanks,

Chloe

  • Huub Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
    Profile
    Send PM
Forum Regular
Threads 1
Posts 185
Multiple possible reasons
Hi Chloe,
I think there can be multiple possible reasons for the behavior you are seeing. Whatever the reason is at convergence the total energy is a minimum for the corresponding orbital occupations. Possible reasons include: the choice of density functional, the use of level shifters, the symmetry of the system, etc.
With regards to the choice of functional this sort of thing is less likely to happen if you pick a functional including exact exchange. Alternatively I would guess that the quasi Newton-Raphson solver is also less likely to produce these kinds of answers.
If you are willing to send me you input I can have a look to see if I can give you some more detailed answers.
Hubertus dot vanDam at PNNL dot gov.

Clicked A Few Times
Threads 5
Posts 21
Hi Huub,

This happened to me both with B3LYP and LDA. I only use DIIS for convergence and always use no symmetry (c1). As for the solver, I use all the defaults (is that Newton-Raphson then ?).

Even if the energy is ok, can I trust the properties computed from the converged density?

I can send you the input file if you want, but it is rather large. The example above is from a calculation that took over a week on a supercomputer.

Thanks for your help,

Chloe


Forum >> NWChem's corner >> General Topics



Who's here now Members 0 Guests 1 Bots/Crawler 0


AWC's: 2.5.10 MediaWiki - Stand Alone Forum Extension
Forum theme style by: AWC