The achieved results involve three main areas:
1. Simulator development
The chosen language is MATLAB® that offers a robust and simple calculation environment, and compatibility with software used by the industry. After robust validation, the generation of C++ portable code, to speed up the code, is under development.
The approach has been set and validated versus experimentally assessed material systems: Si, Ge, GaAs, SiGe alloys. Then, the simulator has been enriched to consider the bipolar effects, important in narrow gap materials or at higher temperatures.
The simulator can account for the full numerical treatment of the following scattering mechanisms for the charge carriers: acoustic phonons, non-polar optical phonons, polar optical phonons, ionized impurities (dopants), alloy. For all of them except the alloy scattering, intra- and inter- valley options are available for the user, with the possibility to account for different parameters for different pairs of initial and final bands, and several optical phonon mechanisms can be included.
Several modules have been implemented to improve the user-friendliness of the simulator, and its use in supercomputing facilities. A Graphical User Interfaces (GUI) for the Input instructions, the scattering file preparation, and the data plot and conversion into .csv files have been developed as well.
A direct interface to the .bsxf files outputted by the XCrysden code has been developed, this allows to interface with some widely used DFT codes (Quantum ESPRESSO, CRYSTAL, WIEN2k). Interfaces with other DFT codes are under development.
The simulator has been applied to the case study of half-Heuslers, one of the most promising and studied class of TE materials. The main scientific results include:
- Demonstration of the importance of the proper treatment of the scattering physics in the materials ranking and best doping evaluation.
- Identification of the materials descriptors that drive TE performances.
- Observation of the unexpected high power factors in narrow bandgap semiconductors.
2. Networking
This activity aimed to enlarge the scientific network of the Experienced Researcher, promote his reputation in the community, advertise the simulator. The networking involved:
- Invited seminar, Univ. of York, 30 Aug. 2018
- Invited seminar, CNR, Chieti, 19 Feb. 2019
- GiTe2019, Bologna, 20-21 Feb. 2019
- MRS - Spring Meeting, Phoenix, AZ, 22-26 Apr. 2019
- IWCN - International Workshop of Computational Nanotechnology, Evanston, IL, 20-24 May 2019
- ECT , Cyprus, 23-25 Sept. 2019
- New Horizons in Materials Modelling, York, 10 Jan. 2020 (with side meetings for feedback in the development of the code attended by the PI, Fellow and faculty at York)
- APS – March Meeting, 2-6 March 2020, uploaded presentation (meeting cancelled for COVID-19).
- VCT – Virtual Conference on Thermoelectrics, 21-23 July 2020, substituting the International Conference on Thermoelectrics (ICT) that should have been hold in Seattle.
The simulator raised interest, especially the part related to the electronic transport properties, which is the first of its kind.
3. Exploitation, dissemination, public engagement
These activities include publications in international peer-reviewed journals, presentations at international conferences, workshops, and public engagement initiatives, code release.
Publications
- “Impact of the scattering physics on the power factor of complex thermoelectric materials”, J. Appl. Phys., 126, 155701 (2019).
- “Effective masses in complex band structures, a code to extract them”, arXiv preprint arXiv:1912.10924 (2019).
- “Material descriptors for the discovery of efficient thermoelectrics”, ACS Appl. Energy Mater. 3, 5913 (2020).
- “Ultra-High Thermoelectric Power Factors in Narrow Gap Materials with Asymmetric Bands”, J. Phys. Chem. C, DOI: 10.1021/acs.jpcc.0c05457 .
- “Carrier Scattering engineering in half Heusler thermoelectrics from first-principles”, in preparation.
Conferences and workshops
See Networking at point 2.
Public engagement:
- Science Festival in Cheltenham, 4-9 June 2019
- British Science Festival (Family Day), 14 Sept. 2019
Code release: The simulator is released open source under the GPL_v3 on the project web page at the University of Warwick and on the Psi-k platform. The essential documentation is provided. The code is planned to be released by September 2020.
