Contents:

FeSe_*kbar.struct - input files for WIEN2k to reproduce the DFT calculations of FeSe0.82S0.18 for each pressure, as given in the filename. For further details of the calculations, see submission_script.arc included with Figure S13 SI. 

FeSe_x*.struct - input files for WIEN2k to reproduce the DFT calculations of FeSe(1-x)Sx for x=0, 0.04, and 1, as given in the filename - x=0.18 is identical to p=0 from the pressure series. 

ShiftsAndRenorms_*kbar.dat - shifts and renormalisations used to fit the raw DFT Fermi surface to experimental quantum oscillations for a variety of pressures. For the format and meaning of the file, see README for Figure S13 SI. The experimental QO data used for this fitting is that shown in Table S2. Where masses are not available for a given pressure, the mass from the next highest pressure was used for the fitting.

ShiftsAndRenorms_x*.dat - shifts and renormalisations used to fit the raw DFT Fermi surface to experimental quantum oscillations for x=0, 0.04, and 1. The experimental QO data used for this fitting is from: 
x=0: 10.1103/PhysRevB.92.121108 (Sample S5) and 10.1103/PhysRevB.90.144517
x=0.04: 10.1038/s41535-018-0141-0
x=1: 10.1103/PhysRevB.90.144517

*_vs_p.dat - files containing data extracted from shifted DFT calculations at several different pressures. The variable extracted is contained within the file name. 

*_vs_x.dat - files containing data extracted from shifted DFT calculations at several different compositions: x=0, 0.04, 0.18, 1. x=0.18 is identical to p=0 in the *_vs_p data. 