Post on 29-Jan-2016
Graphene on Ir(111) surface: interplay between chemical bonding and
van der Waals
Predrag Lazić, Nicolae Atodiresei, Vasile Caciuc, Radovan Brako and Stefan Blügel
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
INSTITUT FÜR FESTKÖRPERFORSCHUNG (IFF) , FZ JÜLICH
RUDJER BOSKOVIC INSTITUTE
plazic@mit.edu
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
MOTIVATION: Experiment
Structure – Moiré 10×10 Graphene on 9×9 Iridium (111)
Typical STM images (there are also “strange” ones)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
Straightforward calculation – 4 layers of Iridium (324 atoms)- graphene 200 C atoms
Rather large supercell
Cutoff 400 eV
3×3 k-points
VASP
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
Straightforward calculation – 4 layers of Iridium (324 atoms)- graphene 200 C atoms
Rather large supercell
Cutoff 400 eV
3×3 k-points
VASP
BUT PROBLEM OCCURS! WE GET NO BINDING IN GGA (PBE)!
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
Straightforward calculation – 4 layers of Iridium (324 atoms)- graphene 200 C atoms
Rather large supercell
Cutoff 400 eV
3×3 k-points
VASP
BUT PROBLEM OCCURS! WE GET NO BINDING IN GGA (PBE)!
MOST PROBABLE CAUSE LACK OF vdW INTERACTION!
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Two ways out of the problem but within DFT framework
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Two ways out of the problem but within DFT framework
Use LDA
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Two ways out of the problem but within DFT framework
Use LDA Use some nonlocal density Functional like vdW-DF (2004)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Two ways out of the problem but within DFT framework
Use LDA Use some nonlocal density Functional like vdW-DF (2004)
Numerically cheapNumerically (very) expensive
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Two ways out of the problem but within DFT framework
Use LDA Use some nonlocal density Functional like vdW-DF (2004)
Numerically cheapNumerically (very) expensive
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
vdW-DF (Dion et al.)M. Dion, H. Rydberg, E. Schröder, D.C. Langreth and B.I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)
Nonselfconsistent implementation (post processing – i.e. no forces for relaxation!)
Trick – for relaxation we use Grimme’s semiempirical approachAnd for the final position we run a vdW-DF energy calculation with our JuNoLo code.Lazić P. et al. 2010 Comput. Phys. Commun. 181 371
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Grimme’s approach for forces (relaxation) + vdW-DF for energy (only at final relaxed position)
Grimme theory – semiempirical one, two coeffiecients for each element C6 and R0.S. Grimme J. Comput. Chem. 27, 1787 (2006)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Grimme’s approach for forces (relaxation) + vdW-DF for energy (only at final relaxed position)
Grimme theory – semiempirical one, two coeffiecients for each element C6 and R0.S. Grimme J. Comput. Chem. 27, 1787 (2006)
Minor problem C6 is not given for Ir.
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
Grimme’s approach for forces (relaxation) + vdW-DF for energy (only at final relaxed position)
Grimme theory – semiempirical one, two coeffiecients for each element C6 and R0.S. Grimme J. Comput. Chem. 27, 1787 (2006)
Minor problem C6 is not given for Ir.
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
LACK OF vdW IN “STANDARD” DFT
C6 for Ir, we determined by:
-Comparing adsorption of Bz on Ir(111) (energies) calculated with Grimme’s approach and vdW-DF calculation
-Comparing Grimme’s approach and vdW-DF for 1x1 commensurate Ir/GrapheneCell (compressed Iridium)
-Final check for C6, calculation of energy with vdW-DF for final configuration of a big (9×9/10×10) cell.
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
THEORETICAL DFT STRUCTURE WITH vdW
dzC=3.4±0.2 Å
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
THEORETICAL DFT STRUCTURE WITH vdW
Adsorption energy (per C atom, in graphite ~-50 meV):
EGGA=+20 meV
Etotal=-44 meV (vdW-DF, PBE exchange) Etotal=-50 meV (Grimme, so Ir C6 is quite OK!)
If we use revPBE for exchange (as vdW-DF suggests) we getEtotal=-11 meV
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
THEORETICAL DFT STRUCTURE WITH vdW
Adsorption energy (per C atom, in graphite ~-50 meV):
EGGA=+20 meV
Etotal=-44 meV (vdW-DF, PBE exchange) Etotal=-50 meV (Grimme, so Ir C6 is quite OK!)
If we use revPBE for exchange (as vdW-DF suggests) we getEtotal=-11 meV
Very interesting result – graphene buckling alone costs almost no energy!0.2 meV per C atom only! (~0.4 Å corrugation)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURE
Even though graphene is dominantly vdW binded there is some charge transfer in the system from graphene to Ir(111).
p-doped graphene
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURECharge transfer
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURECharge transfer
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURECharge transfer
Shift of Dirac’s cone +0.2 eV
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURENonlocal binding energy (almost as seeing vdW!)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
ELECTRONIC STRUCTURENonlocal binding energy (almost as seeing vdW!)
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
GROWTH, NOT SPOTTING THE PROBLEM TILL THE FULL MONOLAYER
n=19
Ref. [1] P. Lacovig et al., Phys. Rev. Lett. 103 166101 (2009).
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals
CONCLUSIONS
GGA is incapable of describing this system properly
Van der Waals interaction plays an important role
vdW-DF is too expensive for such a system to be used directlybut in combination with semiempirical method seems to give goodresults so that is the approach that should be considered for other systemsin which vdW plays a significant role
2010 APS March Meeting March 15–19, 2010; Portland, Oregon
Graphene on Ir(111) surface: interplay between chemical bonding and van der Waals