[Pw_forum] How to adjust emass,dt and cutoff in cp.x calculation?

[Ruijuan Xiao]

Dear all,
I met some problems when I do some calculations by cp.x. What I calculated is a cubic box in which 54 Na atoms exist. When I use dt=5.0d0, emass=400.0d0, and emass_cutoff=3.0d0, it can run without any problems. When I put dt=5.0d0,emass=400.0d0, then change the value of emass_cutoff, the calculation also runs without problems.

But when I put emass=400.0d0 and emass_cutoff=3.0d0,then change dt into 10.0d0, the following error message appears and the program stopped.
-----------------------------------
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     from ortho : error #        21
     max number of iterations exceeded
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     stopping ...
------------------------------------

When I put dt=5.0d0 and emass_cutoff=3.0d0, but change emass into 200.0d0, the program stopped after 12 iterations. The message is :
------------------------------------
  nfi    ekinc  temph  tempp        etot      enthal       econs       econt    vnhh   xnhh0    vnhp   xnhp0
   10 ********    0.0    0.0    41.82500    41.82500    41.82500   146.23636  0.0000  0.0000  0.0000  0.0000
   11  NaN        0.0    0.0    58.16717    58.16717    58.16717  NaN         0.0000  0.0000  0.0000  0.0000
   12  NaN        0.0    0.0  NaN         NaN         NaN         NaN         0.0000  0.0000  0.0000  0.0000

   MAIN:          EKINC   (thr)          DETOT   (thr)       MAXFORCE   (thr)
   MAIN:  NaN            0.1D-03 NaN            0.1D-08  0.000000D+00  0.1D+11
   MAIN: convergence achieved for system relaxation


              averaged quantities :
         ekinc          ekin          epot          etot     tempp
 NaN           NaN           NaN           NaN                 0.0
-----------------------------------
It seems that the calculation is sensitive to these parameters. Since on the page 37 of the maunal, it says that "unless you are already experienced with the system you are studying or with the code internals, usually you need to tune some
input parameters, like emass, dt, and cut-offs.", so these parameters must be important for calculations, but now I am puzzled about how to adjust emass,dt and cutoff in cp calculations.Would you like to give me any information or any suggestion about that?

Thank you very much.


Best regards,

Sincerely,
Ruijuan Xiao
Institute of Physics,
Chinese Academy of Sciences