Links from internet
Saw-tooth potential in Quantum Espresso
Link 1
Link 2
Modern theory of polarization
Useful Linux commands
Joining multiple files and compressing without losing quality
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input1.pdf input2.pdf input3.pdf input4.pdf