ACCURACY OF DFT CALCULATIONS IN THE DISSOCIATION OF N2/W(110)
G.A. Bocan, R. Díez Muiño, M. Alducin, H.F. Busnengo, and A. Salin
Donostia International Physics Center (DIPC) San Sebastián, Spain
MOLECULAR DYNAMICS
MOLECULAR DYNAMICS
Direct Reflection
MOLECULAR DYNAMICS
Direct dissociative sticking
MOLECULAR DYNAMICS
Dynamic Trapping
HOW AND WHY
System: N2 / W(110) (large crystallographic anisotropies)
Build the 6D Potential Energy Surface (PES)+
Classical molecular dynamics
DFT calculations (VASP): Grid of 5610 6D points
Interpolation: Corrugation Reducing ProcedureThe PES
XC modeled by a GGA functional Adiabatic approximation Frozen surface
DFT not exact!!
Only reflection & dissociative sticking allowed
DYNAMICS: PW91 vs. RPBE
Theoretical prediction(PW91 XC functional in the PES)
Alternative RPBE XC functional Better fit to experimental
chemisorption energies Better description very
near the metallic surface Better dynamics??
Theoretical prediction
(RPBE XC functional in the PES)H.E. Pfnür et al., JCP 85 7452 (1986)C.T. Rettner et al., JCP 93, 1442 (1990)M. Alducin et al., PRL 97, 056102 (2006)
NORMAL INCIDENCE
PW91 RPBE
Ei = 0.4 eV, 5000 trajectories
60o INCIDENCE
PW91 RPBE
Ei = 0.9 eV, 5000 trajectories
CONCLUSIONS
The differences between RPBE and PW91 results are a measure of the PES DFT calculation accuracy.
RPBE higher medium distance barriers make it more difficult for incoming trajectories to reach the precursor well, thus ensuring a better fit to experiments in normal incidence but also a poor prediction for the 60o incidence case.
THE END(Thank you for your attention!)
BACK TO THE PES
Top
Hollow
Bridge
Long Top-Hollow