Wider research context / theoretical framework

Symmetry is one of the pillars of fundamental physics, chemistry, and materials science. A model crystal is defined by the repetition of an atomic motif on each of the nodes of a 3D periodic lattice, whose three discrete translation symmetries give rise to the electronic and vibrational bands of crystalline solids. Those bands underpin all of solid-state theory; in particular, thermal transport properties reflect the features of the space group, combining the three translations and the point group of the motif.

As part of the current nano-revolution, materials based on 1D structures like nanotubes have emerged as natural candidates for many chemical structural and microelectronic applications. Although these structures exist in 3D space, their symmetries include a single translation. Therefore, they must be studied in terms of line groups instead of space groups.

Hypotheses / research questions / objectives

PULGON aims to lay the foundations for the study of thermal transport properties of 1D nanostructures, starting from a comprehensive description of their symmetry operations. In particular, it will extend existing formalisms with an implementation of line groups. Four specific applications will be tackled: thermal transport in Si and Ge nanowires; interfaces between III-V nanowires; the phonon properties of ternary and Janus chalcogenides, and strongly anharmonic thermal transport in multiwall nanotubes.

Approach / methods

PULGON will create a library able to detect the line group of a particular 1D crystal with a predefined tolerance and implement the character tables of the 13 families of line groups. Those are the essential ingredient to build the projection operators required to study band structures and transport from a symmetry-adapted perspective. The library will be integrated with almaBTE, created by the PI, to tackle the aforementioned applications. To overcome the limited scalability of first-principles calculations, machine-learning force fields will be trained using the NeuralIL package.

Level of originality / innovation

Existing quantum chemistry packages focus on non-periodic systems (point groups, e.g. molecules), fully periodic systems (space groups, 3D crystals) or both. PULGON will enable the systematic study of transport in subperiodic systems. By removing the artifacts introduced when improperly applying 3D methods to such important systems and nanotubes and nanowires, it will provide precise answers to open questions those. Moreover, by harnessing symmetries to the maximum, it will deliver large performance gains in the description of 1D crystals.

Primary researchers involved

PI duties will be carried out by Dr. Jesús Carrete Montaña at the Institute of Materials Chemistry at TU Wien. Two PhD students will be hired as part of the project to work on the development and applications of the formalism.