Metal convergence problem

sdTurb · 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.

uwe · November 02, 2010, 11:41:19 AM

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

Metal convergence problem

sdTurb

uwe