First-principles studies on traditional and emerging materials

Scientists from the Computational Materials Science Group, National Technical University of Athens (NTUA) have used the HellasGrid Infrastructure and the EGI Grid infrastructure in order to solve problems coming from the area of density-functional theory (DFT). Specifically, they used the Vienna Ab Initio Simulation Package (VASP), a widely used code that performs so-called first-principles calculations on materials within the framework of density-functional theory (DFT).

The employment of traditional and emerging materials in technological applications presupposes a detailed knowledge of their physical properties. An accurate description of these properties at the atomic-scale is linked to the solution of quantum-mechanical (QM) differential equations, a task of immense challenges due to interactions among electrons in extended systems. DFT codes such as VASP utilize one of the most popular theoretical approaches, the so-called density-functional theory, to solve the QM equations and describe, thus, the electronic, chemical, mechanical, optical, or transport properties of a plethora of physical systems (bulk solids, surfaces, nano-systems of different dimensionality, molecules, etc).

Figure 1 - Energy variation during diffusion of a C dopant in TiO2

The scientists from the Computational Materials Science Group have undertaken a number of investigations [1-8] using the HellasGrid infrastructure to perform DFT calculations. These studies probed the properties of materials that have attracted strong interest in recent years. Examples include TiO2, a material with potential use in photovoltaics and photocatalysis,[1], [2] organic semiconductors,[3], [6]  layered hard systems, [4], [5] and materials employed in novel electronic devices. [7], [8] The associated publications [1], [8] provide extensive information on how the detailed knowledge of the QM properties of the above systems can lead to further optimization of related applications.

As VASP is a parallel code that utilizes MPI to distribute the workload to different nodes, first-principles calculations are computationally intensive and the use of a large network of clusters like the HellasGrid is indispensable for this type of studies. The number of nodes required varies from problem to problem, with small jobs typically running on 4-8 nodes, to larger tasks of 32 or more nodes.

DFT calculations are currently underway to probe the properties of several other important materials, such as graphene and other two-dimensional materials, carbon nanotubes, silicon nanowires, organic photovoltaics, and others. The completion of these studies will lead to new publications and boost the scientists’ understanding for systems that play a key role in emerging technologies.

Contacts

  • Leonidas Tsetseris, Assistant Professor, NTUA, leont (at) mail.ntua.gr
  • Georgios Volonakis, PhD candidate, AUTH, gvolo (at) physics.auth.gr
  • Evangelos Golias, PhD candidate, NTUA, vgolias (at) ims.demokritos.gr

References

  1. Stability and dynamics of carbon and nitrogen dopants in anatase TiO2”, L. Tsetseris, Physical Review B 81, 165205 (2010).
  2. Configurations, electronic properties, and diffusion of carbon and nitrogen dopants in rutile TiO2”, L. Tsetseris, Physical Review B 84, 165201 (2011).
  3. Stability of Group-V Endohedral Fullerenes”, L. Tsetseris, Journal of Physical Chemistry C 115, 3528 (2011).
  4. Electronic and structural properties of TiB2: Bulk, surface, and nanoscale effects”, G. Volonakis, L. Tsetseris, and S. Logothetidis, Materials Science and Engineering B 176, 484 (2011).
  5. Excess of boron in TiB2 superhard thin films: a combined experimental and ab initio study”, N. Kalfagiannis, G. Volonakis, L. Tsetseris, and S. Logothetidis, Journal of Physics D 44, 385402 (2011).
  6. “Impurity-related vibrational modes in a pentacene crystal”, G. Volonakis, L. Tsetseris, and S. Logothetidis, European Physical Journal: Applied Physics 55, 23903 (2011).
  7. “Ge volatilization products in high-k gate dielectrics”, E. Golias, L. Tsetseris, A. Dimoulas, and S. T. Pantelides, Microelectronic Engineering 88, 427 (2011).
  8. “Ge-related impurities in high-k oxides: Carrier traps and interaction with native defects”, E. Golias, L. Tsetseris, and A. Dimoulas, Microelectronic Engineering 88, 1432 (2011).