TMDC

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Revision as of 16:30, 13 August 2013

General Information

• Application's name: The electronic structure, optical and transport properties of layered transition-metal dichalcogenides and their intercalated compounds
• Application's acronym: TMDC
• Scientific domain: Computational Physics
• Contact person: Yurii Chumakov, chumakov<>phys.asm.md
• Main Developers: Yurii Chumakov, Institute of Applied Physics Academy of Sciences of Moldova
• Co-developers: -
• Allocation period: period
• Web site:

Objectives of the computing project

The proposed application, which is ready for porting in the HP-SEE infrastructure, numerically investigates the electronic structure, optical and transport properties of layered transition-metal dichalcogenides and their intercalated compounds

See: "Yu. Chumakov, J. R. Santos, I. Ferreira, K. Termentzidis, A. Pokropivny, S.-Y. Xiong, P. Cortona, S. Volz. Ab initio Calculations and Measurements of V2O5 Film Thermoelectric Properties. Journal of Electronic Materials, 2012, Pages: 1-7,DOI: 10.1007

Application's description

Molybdenum and tungsten disulfide and diselenide MX2 (M = Mo and W; X = S and Se), often termed as the MoS2 family, as important members of layered transition-metal dichalcogenides (TMDCs), have attracted a lot of interest because of their intriguing chemical and physical properties. These materials have band gaps falling in the visible or near-infrared light regime so that they are promising for efficient solar-energy conversion.

For a semiconductor to be used in solar-energy conversion, its electronic band structure is one of the most important parameters and determines, among others, the range of the solar spectrum it can absorb. More importantly, the peculiar layered structure of TMDCs makes it possible to fine tune their electronic properties by either introducing foreign atoms or molecules between weakly bonded layers to form various intercalated compounds or forming low-dimensional nanostructured materials. MoS2 and other transition metal dichalcogenide materials were reported to have very pronounced values of thermopower. Van der Waals interaction between weakly bonded layers may enhance some intriguing properties on one hand, while suppressing electrical transport properties on the other.

In the current project we systematically study the electronic structure, optical and transport properties of MoS2 family and intercalated compounds, based on the Boltzmann transport theory and first-principles density functional calculations. VdW corrections to GGA calculations are essential to deal with such compounds. The DFT calculations will be performed using the ABINIT package which calculates the ground state properties, response functions (through DFPT), and even excited states (through the GW approximation or TDDFT) of systems. It employs plane wave basis sets and pseudopotentials from most of the popular families.

The code has been parallelized efficiently and scales well on modern supercomputers because it offers three levels for MPI parallelization:

1. parallel calculation of different k-points (points in the inverse space with the same energy level)

2. parallel calculation of different bands

3. parallel FFT (fast Fourier Transformation)

Results expected in the allocation period

The electronic structure, optical and transport properties of MoS2 and its intercalated compounds will be studied.

Activity report

The strong bound exciton luminescence of the TMDCs layered compound is due to the neutral centres formed by halogen molecules intercalated in the interstitial sites of the van der Waals gap during the growth of the synthetic crystals. The X-ray analysis showed that there are two polymorphs forms of MoS2 which are denoted as 2H (I) and 3R (II) (Fig. 1). For these forms we investigated the effect of interlayer interactions on the band structure and density of states using ABINIT package [1]. It employs plane wave basis sets and pseudopotentials from most of the popular families.

The code has been parallelized efficiently and scales well on modern supercomputers because it offers three levels for MPI parallelization and calculations were performed on HPCG.

It was shown that the strong photoluminescence of these indirect band gap semiconductors I and II is caused by recombination of excitons bound to the neutral centres formed by halogen molecules intercalated in the well-defined sites of the van der Waals gap. These centers, located at energy below the conduction band.

It is planned to prepare the paper based on these calculations where acknowledgments related on results obtained with the help of the HP-SEE infrastructure will be included.

Figure 1. The band structures of MoS2- 2H (I) and MoS2-3R (II) compounds.

[1] Gonze, J.-M. Beuken, R. Caracas, F. Detraux, M. Fuchs, G.-M. Rignanese, L. Sindic, M. Verstraete, G. Zerah, and F. Jollet, et al., Comput. Phys. Commun. 180, 2582 (2009).