TURBOMOLE Users Forum
TURBOMOLE Modules => Ridft, Rdgrad, Dscf, Grad => Topic started by: sdTurb on October 29, 2010, 01:26:29 PM
-
I am currently running DFT calculations on gold contacts with a CRENBS ECP basis set and PBE functional with grid size m3.
Trying to converge the calculation without any hole states is proving difficult.
When using Fermi smearing i obtain a negative HOMO-LUMO energy gap with a hole state as below
Total energy = -143.9210604175 H = -3916.2935434 eV
HOMO-LUMO Separation
HOMO: 272. 271 a -0.08983662 H = -2.44458 eV
LUMO: 270. 272 a -0.09064732 H = -2.46664 eV
Gap : -0.00081070 H = -0.02206 eV
!! WARNING: HOMO-LUMO Gap is negativ !!
Number of MOs= 542, Electrons= 542.00, Symmetry: c1
Nr. Orbital Occupation Energy
287. 287 a -0.075128 H = -2.044 eV
286. 286 a -0.075138 H = -2.045 eV
285. 285 a -0.079585 H = -2.166 eV
284. 284 a -0.079626 H = -2.167 eV
283. 283 a -0.081439 H = -2.216 eV
282. 282 a -0.081542 H = -2.219 eV
281. 281 a -0.084276 H = -2.293 eV
280. 280 a -0.084327 H = -2.295 eV
279. 279 a -0.084414 H = -2.297 eV
278. 278 a -0.087521 H = -2.382 eV
277. 277 a -0.088287 H = -2.402 eV
276. 276 a -0.088885 H = -2.419 eV
275. 275 a -0.089466 H = -2.434 eV
274. 274 a -0.089691 H = -2.441 eV
273. 273 a -0.089834 H = -2.445 eV
272. 271 a 2.000 -0.089837 H = -2.445 eV
271. 270 a 2.000 -0.090052 H = -2.450 eV
270. 272 a -0.090647 H = -2.467 eV
269. 269 a 2.000 -0.090737 H = -2.469 eV
268. 268 a 2.000 -0.095203 H = -2.591 eV
267. 267 a 2.000 -0.096041 H = -2.613 eV
266. 266 a 2.000 -0.096473 H = -2.625 eV
265. 265 a 2.000 -0.098099 H = -2.669 eV
264. 264 a 2.000 -0.099244 H = -2.701 eV
263. 263 a 2.000 -0.100215 H = -2.727 eV
262. 262 a 2.000 -0.100449 H = -2.733 eV
261. 261 a 2.000 -0.100481 H = -2.734 eV
260. 260 a 2.000 -0.101488 H = -2.762 eV
259. 259 a 2.000 -0.101563 H = -2.764 eV
258. 258 a 2.000 -0.103084 H = -2.805 eV
257. 257 a 2.000 -0.104116 H = -2.833 eV
256. 256 a 2.000 -0.104190 H = -2.835 eV
255. 255 a 2.000 -0.105680 H = -2.876 eV
On another thread i read about the $lastdiag option as a possible solution.
When i implement the $lastdiag option it eliminates the negative HOMO-LUMO gap but shifts the LUMO orbitals resulting in a large positive HOMO-LUMO gap too big for a metal contact as can be seen below. (I have more severe examples of this even up to 5-6ev gap)
I cant seem to solve this problem with either approach.
Total energy = -143.9209569997 H = -3916.2907293 eV
HOMO-LUMO Separation
HOMO: 271. 271 a -0.08962911 H = -2.43893 eV
LUMO: 272. 272 a -0.02712896 H = -0.73822 eV
Gap : +0.06250014 H = +1.70072 eV
Number of MOs= 542, Electrons= 542.00, Symmetry: c1
Nr. Orbital Occupation Energy
288. 288 a -0.004102 H = -0.112 eV
287. 287 a -0.011500 H = -0.313 eV
286. 286 a -0.011515 H = -0.313 eV
285. 285 a -0.015932 H = -0.434 eV
284. 284 a -0.015986 H = -0.435 eV
283. 283 a -0.017821 H = -0.485 eV
282. 282 a -0.017978 H = -0.489 eV
281. 281 a -0.020789 H = -0.566 eV
280. 280 a -0.020849 H = -0.567 eV
279. 279 a -0.020876 H = -0.568 eV
278. 278 a -0.023880 H = -0.650 eV
277. 277 a -0.024737 H = -0.673 eV
276. 276 a -0.025506 H = -0.694 eV
275. 275 a -0.026002 H = -0.708 eV
274. 274 a -0.026009 H = -0.708 eV
273. 273 a -0.026191 H = -0.713 eV
272. 272 a -0.027129 H = -0.738 eV
271. 271 a 2.000 -0.089629 H = -2.439 eV
270. 270 a 2.000 -0.090226 H = -2.455 eV
269. 269 a 2.000 -0.090767 H = -2.470 eV
268. 268 a 2.000 -0.095126 H = -2.589 eV
267. 267 a 2.000 -0.095983 H = -2.612 eV
266. 266 a 2.000 -0.096415 H = -2.624 eV
265. 265 a 2.000 -0.098040 H = -2.668 eV
264. 264 a 2.000 -0.099593 H = -2.710 eV
263. 263 a 2.000 -0.100158 H = -2.725 eV
262. 262 a 2.000 -0.100397 H = -2.732 eV
261. 261 a 2.000 -0.100429 H = -2.733 eV
260. 260 a 2.000 -0.101295 H = -2.756 eV
259. 259 a 2.000 -0.101624 H = -2.765 eV
258. 258 a 2.000 -0.103021 H = -2.803 eV
257. 257 a 2.000 -0.104154 H = -2.834 eV
256. 256 a 2.000 -0.104294 H = -2.838 eV
I am using Turbomole 6.1. Any insight would be greatly appreciated.
-
Hi,
for such a tiny gap the $lastdiag should indeed solve the problem with negative gaps, but you could also consider to increase the gridsize for DFT and/or SCF and density convergence - there are a LOT of unoccupied orbitals with more or less the same energy as the HOMO...
Please note that the 'negative' gap for such small differences is not really a problem but just a numerical artifact - the total energy is correct. It is, however, a hint for a possible multi-reference case. And for TDDFT it is awkward since escf and egrad will complain in such cases.
The really puzzling thing is the huge gap if you use $lastdiag. It looks like an output error - could be that the orbital shift has not been undone in your case. What is the entry of the $scforbitalshift keyword in the control file?
Also, how does your CRENBS ECP basis set look like? I have just checked it in EMSL basis set library and it seems that the basis set is not correct there - just a dummy set for the ECPs and not an optimized one... So if you took CRENBS from there, the results will be very strange anyway.
Regards,
Uwe