-------------------------------------------------------------------------------- ### Influence of germanium substitution on the structural and electronic stability of the competing vanadium dioxide phases -------------------------------------------------------------------------------- Peter Mlkvik, Claude Ederer, and Nicola A. Spaldin -------------------------------------------------------------------------------- #### Abstract: We present a density-functional theory (DFT) study of the structural, electronic, and chemical bonding behavior in germanium (Ge)-doped vanadium dioxide (VO2). Our motivation is to explain the reported increase of the metal-insulator transition temperature under Ge doping and to understand how much of the fundamental physics and chemistry behind it can be captured at the conventional DFT level. We model doping using a supercell approach, with various concentrations and different spatial distributions of Ge atoms in VO2. Our results suggest that the addition of Ge atoms strongly perturbs the high-symmetry metallic rutile phase and induces structural distortions that partially resemble the dimerization of the experimental insulating structure. Our work, therefore, hints at a possible explanation of the observed increase in transition temperature under Ge doping, motivating further studies into understanding the interplay of structural and electronic transitions in VO2. -------------------------------------------------------------------------------- All calculations were performed using the Quantum Espresso code (version 6.4.1), using the PBE exchange-correlation functional. The main folder contains input files for all calculations presented in the paper, with subfolders indicating which part of the paper the data corresponds to. Folder "222" contains data for the smaller supercell calculations, including the inputs necessary for the calculation using the BandUP code as discussed in the paper. Folders "223-m1" and "223-r" correspond to the two VO2 phases, and include inputs for all the different Ge-doping configurations studied, labelled using numbers "1" and "0" depending on the position of the given Ge atom, separating the columns in the structure by dots (i.e. "110000.00000" corresponds to two Ge atoms in a single chain right above each other, "101000.000000" corresponds to having one V in between etc.).