Hi Eduardo default values should be in a reasonable range, but I am not sure that the default for "fnosee" was the subject of much thought: 1 THz seems to me a small value. So don't assume that your estimate is wrong and the default is right. Note also that there is a small section in the user guide (CPV/Doc/user_guide.pdf) about Nosé thermostats for electrons.
If you have well separated phonon energies, you may need to use several Nosé thermostats for ions as well, I think, but I have no experience about this. Paolo On Sun, Oct 14, 2018 at 5:01 PM Eduardo Menendez <earie...@gmail.com> wrote: > Hi fellows, > I am exploring the Car Parrinello dynamics for a system with hydrogens: > CH3NH3PbI3. With N-H vibrations faster than 3000 cm^-1 and a > fluctuating bandgap that may be as small as 1.5 eV , I guess I will need > to use a thermostat for the electrons, in order not to use a very small > emass and dt. > Estimating a minimum electronic frequency sqrt(2Eg/emass), using the > default emass=400, I get omega_min~0.016 atomic units. For the N-H > vibrations, the frequency is 3000 cm^ -1~ 0.014 atomic units . > I read elsewhere than a good frequency for the electron thermostat is 2-3 > times the maximum phonon frequency (90THz), this led me to the value > fnosee=270.0 > My guess is 270 times larger than the default value fnosep=1.D0. Running > in a parameter space different to what is tested is generally not a good > idea. Am I missing something ? > > A related, but independent question is about the ion thermostat. > The vibrational frequencies of this system are very well separated: ~3000 > cm^-1 for N-H and C-H, > 900-1200cm^-1 for CH3NH3 molecular vibrations, and <300 cm^-1 for others. > Hence, should I set an intermediate fnosep=30.0 (1000 cm^-1), or should I > set a Nose-Hoover chain with frequencies close to every phonon band, e.g., > fnosep=90.0 30.0 10.0 3.0 > > Thanks a lot, > > Eduardo Menendez Proupin > University of Chile > www.gnm.cl/emenendez > _______________________________________________ > users mailing list > users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users -- Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
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