Dear All,
I am nowadays performing some benchmark calculations about bulk
TiO2 (rutile and anatase). The idea is to do some calculations on different
surface reconstructions.
I think that (I am almost sure) a pseudo for Ti with p orbitals in the
valence is almost mandatory for getting reliable results.
The problem I am facing is the following. I found a pseudo LDA for Ti
in the website of Siesta together with the optimized basis set (Ti
semicore states (3s and 3p) in valence)
For O I use the pseudo I found in the website (Oxygen tm2, distrib with
SIESTA, and a DZP basis set)
When I test the structure of rutile (MD.Variable.Cell false), it is very
difficult for me to get the convergence (more than 1000 CG steps). It
seems impossible indeed to reduce the forces below 0.03 eV/Ang.
This seems to me quite strange, also because I am restarting from a 4x4x1
Gamma centered previously converged structure.
It is impossible that increasing the sampling from 4x4x1 to 4x4x2 the
number of CG changes from 11 to more than 1000.....
I thus think that if convergence is not achieved for this small system
(rutile, only 2 Ti atoms) even more difficult (if not impossible) will be
to perform
calculations on slabs.
Thus I wonder if someone can give me some suggestions in order to fix this
problem. Is it a pseudo problem? Is it sufficient a 4e- pseudo in the
valence for optimally describing TiO2 properties (I am quite doubtful
about it)? I already know form literature that it is very difficult to
reproduce the experimental energetic ordering of anatase and rutile.
In case, has anyone a pseudo tested for Ti (PBE even better) used for TiO2
based systems to share with me?
SystemName TiO2_rutilo
SystemLabel TiO2_rutilo
NumberOfAtoms 6
NumberOfSpecies 2
%block ChemicalSpeciesLabel
1 22 Ti
2 8 O
%endblock ChemicalSpeciesLabel
%block PAO.Basis # Define Basis set
Ti 5 1.91
n=3 0 1 E 93.95 5.20
5.69946662616249
1.00000000000000
n=3 1 1 E 95.47 5.20
5.69941339465994
1.00000000000000
n=4 0 2 E 96.47 5.60
6.09996398975307 5.09944363262274
1.00000000000000 1.00000000000000
n=3 2 2 E 46.05 4.95
5.94327035784617 4.70009988294302
1.00000000000000 1.00000000000000
n=4 1 1 E 0.50 1.77
3.05365979938936
1.00000000000000
%endblock PAO.Basis
%block PAO.BasisSizes
O DZP
%endblock PAO.BasisSizes
XC.functional LDA
XC.authors CA
LatticeConstant 4.59220 Ang
%block LatticeVectors
1.0000 0.000 0.000
0.0000 1.000 0.000
0.0000 0.000 .64435346892556944384
%endblock LatticeVectors
%block kgrid_Monkhorst_Pack
4 0 0 0.5
0 4 0 0.5
0 0 2 0.5
%endblock Kgrid_Monkhorst_Pack
MeshCutoff 100.0 Ry
MaxSCFIterations 1000
DM.MixingWeight 0.05
DM.NumberPulay 3
DM.Tolerance 1.d-4
SolutionMethod diagon
SpinPolarized true
LongOutput true
MD.TypeOfRun cg
MD.NumCGsteps 1000
MD.VariableCell false #true
MD.MaxForceTol 0.01 eV/Ang #0.005 eV/Ang
WriteForces true
WriteCoorCerius true
WriteCoorXmol false
WriteDenchar true
WriteMullikenPop 1
UseSaveData true
Diag.ParallelOverK true
AtomicCoordinatesFormat Fractional
%block AtomicCoordinatesAndAtomicSpecies
0.00000 0.00000 0.00000 1
0.50000 0.50000 0.50000 1
0.30510 0.30510 0.00000 2
0.19490 0.80510 0.50000 2
0.69490 0.69490 0.00000 2
0.80510 0.19490 0.50000 2
%endblock AtomicCoordinatesAndAtomicSpecies
.....
siesta: ==============================
Begin CG move = 1000
==============================
outcoor: Atomic coordinates (fractional):
-0.00002412 0.01663451 -0.00906965 1 Ti 1
0.49999230 0.51667694 0.49093035 1 Ti 2
0.29977119 0.33204697 -0.00156798 2 O 3
0.20023279 0.83205355 0.49848870 2 O 4
0.70023510 0.70128165 -0.00155817 2 O 5
0.79979393 0.20130016 0.49847493 2 O 6
superc: Internal auxiliary supercell: 4 x 4 x 7 = 112
superc: Number of atoms, orbitals, and projectors: 672 10080 11648
outcell: Unit cell vectors (Ang):
4.592200 0.000000 0.000000
0.000000 4.592200 0.000000
0.000000 0.000000 2.959000
outcell: Cell vector modules (Ang) : 4.592200 4.592200 2.959000
outcell: Cell angles (23,13,12) (deg): 90.0000 90.0000 90.0000
outcell: Cell volume (Ang**3) : 62.4003
siesta: iscf Eharris(eV) E_KS(eV) FreeEng(eV) dDmax Ef(eV)
siesta: 1 -4921.3185 -4921.3185 -4921.3185 0.0000 -4.1784
siesta: E_KS(eV) = -4921.3185
siesta: Atomic forces (eV/Ang):
1 0.001276 0.003726 -0.037969
2 -0.000729 -0.003555 -0.039057
3 0.003563 0.007823 0.004704
4 -0.006634 0.009005 -0.003266
5 -0.003276 -0.006490 0.003888
6 0.000690 -0.007992 0.002003
----------------------------------------
Tot -0.005110 0.002516 -0.069698
----------------------------------------
Max 0.039057
Res 0.013671 sqrt( Sum f_i^2 / 3N )
----------------------------------------
Max 0.039057 constrained
Thanks in advance!
Best
Giacomo
* * * * * * * * * * * * * * * * * * * * * * * * *
* Giacomo Giorgi *
* Ph.D. *
* Dipartimento di Chimica e Istituto di *
* Scienze e Tecnologie Molecolari ISTM-CNR *
* Universita' degli Studi di Perugia *
* Via Elce di Sotto 8 06123 Perugia Italia *
* Tel: +39 075-5855618 Fax: +39 075-5855606 *
* E-mail: giac_at_thch.unipg.it *
* * * * * * * * * * * * * * * * * * * * * * * * *
"Oltre le illusioni di Timbuctu'
e le gambe lunghe di Babalu' c'era questa strada...
Questa strada zitta che vola via come una farfalla,
una nostalgia, nostalgia al gusto di curacao...
Forse un giorno meglio mi spieghero'..."
(Paolo Conte, "Hemingway")
