Dear Lihui Ou, > Do pwscf only periodic hybrid density functional theory calculation, > it could do any other general density functional theory calculation? I am not sure if I got the point of your question correctly, but Plane Wave SCF program can only solve systems thorough plane wave approximation, i.e. not through an all-electron calculation, and for simplification purposes (that is, in order to have tangible Fourier transforms etc.) periodicity/symmetries are employed. This is more than acceptable for crystals, but for macromolecules etc, you should be extra careful setting the boundaries (the most simple limit is this: a very big box surrounding the molecule you are interested in will somewhat approximate a standalone molecule, however the size of the box is limited by a combination of how the plane wave approximation is employed in pwscf and bare computational limits, you need to find the optimum value). There are other packages available such as NWChem or Gaussian for all-electron calculations. Pseudo potential wise, you can create a pseudo potential to your desire, as long as you can validify your results. Please see the documentation.
> Is there any principle about setting of k-point and cut-off energy? Well, yes. The idea is: You should minimize the number of k-points and cut-off (and a number of other parameters depending on the system you are studying) in order to save computer time whilst maintaining physically meaningful results. The "physically meaningful result" part depends on your problem, keep in mind that total energy in DFT is not very well defined, due to nature of Kohn-Sham orbitals, only the differences in energy are trustworthy, or the observables, such as unit cell volume. Generally you are advised to do a number of calculations with varied parameters in order to obtain a converged set before starting the problem itself (i.e. if you are using lattice parameter as your observable, find the lattice parameter that minimizes the energy for each ecutwfc-k-point combination. You will see that after a certain limit, your lattice parameter will not change much, that value is the minimum you can use, you may later need to increase it, depending on your problem). > Best wishes > Lihui Ou Hope this was helpful, Best, Osman Baris Malcioglu Ph.D. Candidate METU, Physics Ankara, Turkey
