<div dir="ltr"> <div>Dear all</div><div> </div><div>I am interested in studying the structural, electronic, and optical properties of periodic systems. I used to calculate the gas phase using Gaussian software. Now for the first time, I want to calculate in solid-state by cp2k. I have got some basic questions about periodic calculations. Please forgive me if I am asking very general questions, and so many....! </div><div> </div><div>I want to start from the crystal X-ray structure...you can see it in the attached file!</div><div> </div><div>1) Can I replace some of its atoms with arbitrary atoms? for example F atom instead of H atom... If I can, I must do calculations by cell-opt run type??? or geo-opt is also good?! </div><div> </div><div> 2) As you see in the attached file, in my x-ray unit cell, there are some atoms outside of the box. Should such atoms be deleted before converting the CIF file to XYZ format? or not?</div><div> </div><div>3) Can this structure be investigated in 2D? </div><div> </div><div>4) If I want to investigate the electronic and optical properties of this structure, can I use the single unit cell or should it be in the form of a supercell? Are the properties of the unit cell and supercell different?</div><div> </div><div>5) There is an important physical concept in the solid-state called k point! Is it necessary to enter its keyword ?! or it is set by default...I don't know? Do you think I should enter it in the input file? whether unit-cell or supercell!</div><div> </div><div> </div><div> I am very sincerely eager to get an answer? please. </div><div> </div><div>Thanks a lot for helping</div> </div>