1. Nergiz Özcan Laboratory of Physical Chemistry
Cluster Calculations of ESR Parameters of the Positively Charged Oxygen Vacancy in Bulk Semiconductor Tin Dioxide
Nergiz Özcan
Laboratory of Physical Chemistry
Oulu,

2. Outline why SnO2? cluster model construction ESR parameters results
conclusion

3. Why SnO2? metal oxides are widely used as sensing materials [1,2].
its electric conductivity is sensitive[3]
semiconductor behavior
oxygen vacancies [4]
spin density distribution
[1] B. Adamowicz et.al., Vacuum 82 (2008)
[2] F. Trani, M. Causa, D. Ninno, G. Cantele and V. Barone, Phys. Rev. B 77, (2008)
[3] M. Batzill, U. Diebold, Progress in Surface Sci. 79, , (2005)
[4] G. Pacchioni, A.M. Ferrari, G. Ierano, Faraday Discuss., 1997, 106,

4. In this project construct the cluster models
use different embedded methods
calculate the ESR parameters g and hyperfine tensors A, using DFT within GGA using PBE and PBE0
SVP, TZVP and TZVPP basis sets
energy levels of the impurity states via Kohn-Sham orbital energies of the bulk, VO0 and VO+ structures

5. Cluster model constraction
start with PBC calculation of bulk SnO2
optimized unit cells from periodic calculations are replicated to make a very large cluster in order to set up lattice sites
three different cluster sizes are selected

6. defined as quantum cluster
correspond to imposing the first, second and third layer of tin atoms
in the case of vacancy there is one missing oxygen atom at the center
for VO0 and VO+ , relaxed atom positions were chosen within 5 Å

7. Embedding models Hydrogen termination with ZH* = +2e/3
point-charge embedding to reproduce the periodic Madelung potential
EWALD-ecp embedding with the ECP centers at the borderline
parameter zone
fixed zone
quantum cluster

8. ESR calculations
we calculated A and g-tensors for the VO+ model (S=1/2)
used the the method implemented in the Gaussian code [5,6]
ge=
[5] V.Gomzi, J.N. Herak, Chem. Phys. Lett. 333, (2007)
[6] D.M. Ramo, J.L. Gavartin, A.L. Shluger, Phys. Rev. B 75, (2007)

9. g-tensor
Isotropic g-value as a function of the cluster size with different embedding models. Experimental g-value is 1.89[8] and [9,10]
[8] C. Canevali, N. Chiodini, P. di Nola, F. Morazzoni et al., J. Mater. Chem. 7, 997 (1997)
[9] D. A. Popescu, J.-M. Herrmann et al., Phys. Chem. Chem. Phys. 3, 2522 (2001).
[10] M. Ivanovskaya, P. Bogdanov, F. Gaglia, P. Nelli et al., Sens. Act. B 77, 268 (2001).

10. spin density
spin density for Sn12 EWALD-ecp for VO+ model

11. Hyperfine coupling
convergence of hyperfine coupling Aiso(Sn), Aiso(Oc), Aiso(Op), Aiso(Ocr) for EWALD-ecp model with PBE and PBE0 for the Vo+ system

12. Energy Calculations Ev Ec
TABLE: Semiconducting gap and gap state energies (eV) for the EWALD-ecp and H*-termination models as functions of the cluster
size for the models. Values based on the Kohn-Sham orbital energies obtained using the PBE/PBE0 functional with TZVPP basis Ev IS Ec IS IS
Experimental energy gap value is 3.6 eV[11]
[11] P.G. Harrison, Willet M J. Nature, 1988, Ev IS IS IS
[12] D. M. Ramo et al., Phys. Rev. B 75, (2007)) IS IS Ev IS

13. Conclusion
cluster calculations of ESR g and hyperfine tensors computationally feasible
EWALD-ecp embedded model is more reliable than Hydrogen termination model
point-charge model leads to unreasonable data.
convergence of g value with cluster size and basis set allows verification of the assignment of literature.

14. Acknowledgment Juha Vaara, University of Helsinki
Tapio T. Rantala & Tommi Kortelainen, Tampere Univesity of Technology
Vyactcheslav Golovanov, South-Ukrainian University
University of Helsinki Research Foundation

15. Thank you for your attention.