ES22-Tokar

Author: Tokar, Kamil - Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava Slovak University of Technology in Bratislava, 917 24 Trnava, Slovakia & Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia

Title: Charge ordering mechanism in silver difluoride from first principles

Abstract: Recently it was demonstrated that α-AgF2 (Pbca) structure represents an excellent silver analog of the parent compound of high-Tc superconducting cuprates. The structure consists of layers of spin-1/2 ions with a formally Ag(d9) electronic configuration, where unpaired electrons occupy the dx2−y2 orbitals antiferromagnetically coupled via a superexchange that involves F(p) orbitals. Possibly elimination of the AgF4 layers buckling could result in an enhanced AFM coupling that surpasses the oxocuprates [1]. In the current study, we reveal a competition between the Mott-Hubbard and intervalence charge transfer mechanism of electron localization in AgF2 using the Density Functional Theory (DFT) technique (standard DFT, DFT+U and hybrid DFT functionals) [2]. At reduced temperature and electron correlations α-AgF2 becomes metallic and dynamically unstable with respect to soft phonons that promote charge ordering. We show that charge density wave (CDW) instability is closely related to the Kohn anomaly and Fermi surface nesting. The long advocated KBrF4-type CDW Ag1+/3+F2 structure [3,4] and its facile transformation to the ground state α-Ag2+F2 phase was explained. Interplay between lattice, charge, and spin degrees of freedom in this seemingly simplistic binary metal fluoride was revealed.

Acknowledgment: K.T. and M.D. acknowledge the ERDF, Research and Innovation Operational Program for project (ITMS2014 +: 313011 W085), the Slovak Research and Development Agency (grant No. APVV-18-0168), and Scientific Grant Agency of the Slovak Republic (VG 1/0223/19). P.P. acknowledges the support by Narodowe Centrum Nauki (NCN, National Science Centre, Poland), Project No. 2017/25/B/ST3/02586. W.G. acknowledges Polish National Science Center (NCN) for Beethoven project (2016/23/G/ST5/04320). The computations were carried out using the Aurel supercomputing infrastructure in CC of Slovak Academy of Sciences acquired within the projects ITMS 26230120002 and ITMS 26210120002 supported by the ERDF, and infrastructure of Interdisciplinary Centre for Mathematical and Computational Modelling (ICM), University of Warsaw (Grants No. G62-24, No. GA83-34).

References:
[1] J. Gawraczynski, D. Kurzydłowski, R. A. Ewings, S. Bandaru, W. Gadomski, Z. Mazej, G. Ruani, I. Bergenti, T. Jaron, A. Ozarowski, S. Hill, P. J. Leszczyński, K. Tokár, M. Derzsi, P. Barone, K. Wohlfeld, J. Lorenzana, and W. Grochala, Proc. Natl. Acad. Sci. USA 116, 1495 (2019). [2] M. Derzsi, K. Tokár, P. Piekarz, and W. Grochala, Phys. Rev. B 105, L081113 (2022). [3] C. Shen, B. Žemva, G.M. Lucier, O. Graudejus, J.A. Allman, N. Bartlett, Inorg. Chem. 38, 4570 (1999). [4] K. Tokár, M. Derzsi, and W. Grochala, Comput. Mater. Sci. 188, 110250 (2021).

Other authors: Derzsi, Mariana Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava Slovak University of Technology in Bratislava, 917 24 Trnava, Slovakia; & Piekarz, Przemyslaw Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31342 Kraków, Poland; & Grochala, Wojciech Center of New Technologies, University of Warsaw, 02089 Warsaw, Poland