CRYSTALpytools: A Python infrastructure for the Crystal code

CRYSTALpytools is an open source Python project available on GitHub that implements a user-friendly interface to the Crystal code for quantum-mechanical condensed matter simulations. CRYSTALpytools provides functionalities to: i) write and read Crystal input and output files for a range of calculations (single-point, electronic structure, geometry optimization, harmonic and quasi-harmonic lattice dynamics, elastic tensor evaluation, topological analysis of the electron density, electron transport, and others); ii) extract relevant information; iii) create workflows; iv) post-process computed quantities, and v) plot results in a variety of styles for rapid and precise visual analysis. Furthermore, CRYSTALpytools allows the user to translate Crystal objects (the central data structure of the project) to and from the Structure and Atoms objects of the pymatgen and ASE libraries, respectively. These tools can be used to create, manipulate and visualise complicated structures and write them efficiently to Crystal input files. Jupyter Notebooks have also been developed for the less Python savvy users to guide them in the use of CRYSTALpytools through a user-friendly graphical interface with predefined workflows to complete different specific tasks

Crucial Role of Ni Point Defects and Sb Doping for Tailoring the Thermoelectric Properties of ZrNiSn Half-Heusler Alloy: An Ab Initio Study

In the wide group of thermoelectric compounds, the half-Heusler ZrNiSn alloy is one of the most promising materials thanks to its thermal stability and narrow band gap, which open it to the possibility of mid-temperature applications. A large variety of defects and doping can be introduced in the ZrNiSn crystalline structure, thus allowing researchers to tune the electronic band structure and enhance the thermoelectric performance. Within this picture, theoretical studies of the electronic properties of perfect and defective ZrNiSn structures can help with the comprehension of the relation between the topology of defects and the thermoelectric features. In this work, a half-Heusler ZrNiSn alloy is studied using different defective models by means of an accurate Density Functional Theory supercell approach. In particular, we decided to model the most common defects related to Ni, which are certainly present in the experimental samples, i.e., interstitial and antisite Ni and a substitutional defect consisting of the replacement of Sn with Sb atoms using concentrations of 3% and 6%. First of all, a comprehensive characterization of the one-electron properties is performed in order to gain deeper insight into the relationship between structural, topological and electronic properties. Then, the effects of the modeled defects on the band structure are analyzed, with particular attention paid to the region between the valence and the conduction bands, where the defective models introduce in-gap states with respect to the perfect ZrNiSn crystal. Finally, the electronic transport properties of perfect and defective structures are computed using semi-classical approximation in the framework of the Boltzmann transport theory as implemented in the Crystal code. The dependence obtained of the Seebeck coefficient and the power factor on the temperature and the carrier concentration shows reasonable agreement with respect to the experimental counterpart, allowing possible rationalization of the effect of the modeled defects on the thermoelectric performance of the synthesized samples. As a general conclusion, defect-free ZrNiSn crystal appears to be the best candidate for thermoelectric applications when compared to interstitial and antisite Ni defective models, and substitutional defects of Sn with Sb atoms (using concentrations of 3% and 6%) do not appreciably improve electronic transport properties

VALUTAZIONE IN CAMPO DEI POSSIBILI EFFETTI DELL'OLIO ESSENZIALE DI OCIMUM BASILICUM L. SULLE COMUNITÀ DI NEMATODI A VITA LIBERA DEL SUOLO

Per far fronte ad una crescente richiesta di cibo, l’agricoltura intensiva ci ha condotti ad un sovrasfruttamento delle risorse naturali e all’alterazione del funzionamento dell’ecosistema suolo; questo principalmente a causa dell’abuso di fitofarmaci di sintesi. La Commissione Europea ha perciò adottato il programma New Green Deal, che mira a dimezzare l’uso di tali prodotti nel tentativo di ripristinare o limitare la perdita di biodiversità negli ecosistemi terrestri e acquatici. Gli oli essenziali (OE), attualmente utilizzati prevalentemente in campo farmaceutico e nella cosmesi, possono rappresentare una valida alternativa sia nella protezione di colture che di derrate alimentari da parassiti e malattie. Comunque, nonostante il crescente interesse della comunità scientifica in questo campo, ad oggi, la maggior parte degli studi sugli OE sono stati condotti in vitro su organismi target o al limite su organismi modello, mentre sono del tutto assenti studi sui potenziali effetti degli OE sulle comunità in campo. Per valutare i possibili effetti di uno degli OE attualmente più promettente in agricoltura, è stato allestito un esperimento direttamente in campo con un approccio sperimentale Before-After-Control-Impact e sono stati analizzati gli effetti del trattamento sulla nematofauna a vita libera. In dettaglio, semi di ceci sono stati trattati prima della semina applicando un rivestimento ad alta concentrazione dell’OE di Ocimum basilicum (25% v/v) e la composizione tassonomica e funzionale della comunità è stata monitorata prima e dopo la semina a distanza di 7, 14, 28 e 56 giorni. L’analisi GC-MS della composizione dell’OE ha evidenziato un chemiotipo a metil cavicolo, fenilpropanoide che costituisce oltre il 78% della composizione totale. I dati, ad oggi raccolti, hanno evidenziato che l'OE di O. basilicum, nonostante le alte concentrazioni applicate, non ha avuto significativi effetti sulla diversità tassonomica e funzionale della nematofauna corroborando il suo possibile utilizzo come prodotto green

Experimental and computational study of the role of defects and secondary phases on the thermoelectric properties of TiNi1+xSn (0 ≤ x ≤ 0.12) half Heusler compounds

Funding Information: Authors acknowledge the CINECA award under the ISCRA initiative, for the availability of high-performance computing resources and support. S. Casassa, L. Maschio, M. Baricco and A. Castellero acknowledge support from the Project CH4.0 under the MUR program “Dipartimenti di Eccellenza 2023-2027” (CUP: D13C22003520001). Publisher Copyright: © 2023 IOP Publishing Ltd.The half Heusler TiNiSn compound is a model system for understanding the relationship among structural, electronic, microstructural and thermoelectric properties. However, the role of defects that deviate from the ideal crystal structure is far from being fully described. In this work, TiNi1+xSn alloys (x = 0, 0.03, 0.06, 0.12) were synthesized by arc melting elemental metals and annealed to achieve equilibrium conditions. Experimental values of the Seebeck coefficient and electrical resistivity, obtained from this work and from the literature, scale with the measured carrier concentration, due to different amounts of secondary phases and interstitial nickel. Density functional theory calculations showed that the presence of both interstitial Ni defects and composition conserving defects narrows the band gap with respect to the defect free structure, affecting the transport properties. Accordingly, results of experimental investigations have been explained confirming that interstitial Ni defects, as well as secondary phases, promote a metallic behavior, raising the electrical conductivity and lowering the absolute values of the Seebeck coefficient.Peer reviewe