<div dir="ltr">Hi Herbert, just a bit about how CP2K works which shines light on your disappointing experience: CP2K still uses a plane wave basis to compue the electrostatic energy (because it is easy and cheap in PW). This automatically means make your box larger and your cutoff higher will increase the cost of the calculation. Hence, vacuum is not for free in CP2K (not quite sure how any of your other codes react when you put in such a cell). Nevertheless, using Gaussians as a primary basis for the other contributions (localized basis sets are cheap for the rest, see QUICKSTEP paper) at least the size wavefunction coefficients matrix is independent of the system size. If you have a look at the timing reports you will see all time is spend in the FFT. I can tell you from experience going to real system the FFT becomes very soon neglegible. The system you use for testing is not really good as a benchmark for speed. As I said above every aproach has its ups and downs. Take that system as an overall performance benchmark and you will find PW codes (VASP, CPMD, CP2K,...) are the worst DFT codes ever while Gaussian based codes are as close to heaven as you can get. And indeed, for (smaller) molecular systems that is the truth but not if you go to larger periodic systems. If you want to get a feeling for the speed of different codes give them a chance to perform at what they are good in. Try once the 32/64/... water benchmark (better done in parallel but could work in serial as well). That gives a bit a feeling for how the code performs on real dense periodic systems. Another point you wrote is: > but some of the systems are sparse, so using a non-PW basis should improve things As written above that doesn't matter too much for CP2K. True, vacuum only affects the FFT part and if that is neglegible in the overall timings, vacuum is for free. But also dense systems benefit from the mixed basis aproach (try the benchmark). Another point is that CP2K is meant to be a parallel code. We can't help it that systems of a given size become somewhat expensive. What we can do is try to make everything as parallel as possible. If you go parallel you can 'easiliy' go up to systems with 1000 atoms and get your answer by tomorrow (or after a coffee break, as always it depends on what you are doing and on how much coffee you drink). That's good about CP2K. Its worst bit you have already said no k-points. That means you won't get away with small systems. As always which code to use depends on what you are interested in. For crystals and surfaces (and other things for sure but I am not an expert) VASP is neat, it has heaps of features (properties it can compute,...) and in combination with k-points allows for smaller unit cells,... If thats what you want, great choice of code. If you want to study adsorption or interfaces (which can become very big) you might want to use different codes (OK, I admit I meant CP2K here) which allow you to simulate systems of the necessary size. Finally the thing I wouldn't do is a mixed use of codes. Yes, it is DFT in both cases but every code has its special bits. Basis set dependece of the results, pseudos,... you really have to make sure that your results are transferable with the settings used in the two codes. And that usually ends up doing the same study with two codes, which means twice the ammount of work. Don't get me wrong, it is definitely a good idea if you get strange or unexpected stuff to check it with a different code/setup. I only say in my oppinion it is better to decide in the beginning for a code and stick to it so your results are consistent (again there can be exceptions). Flo PS: Just to make sure, I wrote this to indicate what CP2K is good/meant for as it seems there was a bit of a misunderstanding and not to start a this code is better han that code war. </div>