[Pw_forum] Cell optimization converges to unrealistic value
YVVishnevsky at yandex.ru
Fri Oct 12 12:40:21 CEST 2012
Dear Giuseppe and all others,
first of all, sorry for the duplicated message in the list. I have not
received any message to my initially registered e-mail address and was
already thinking that my question has not got into the pw_forum.
> Dear Yuri
> There are technical and physical reasons behind your unrealistic results.
>> N 14.00700 N.pbe-van_ak.UPF
>> H 1.00800 H.pbe-van_ak.UPF
>> C 12.01100 C.pbe-van_ak.UPF
>> Cu 63.54600 Cu.pbe-n-van_ak.UPF
>> ecutwfc = 25 ,
>In the case of ultrasoft pseudopotential ecutrho has to be indicated,
>having a value between
>6*ecutwfc and 10*ecutwfc (convergence should be reached with respect
>to all such values, but I
>perform satisfactorily converged CuPc calculations with the same
>pseudos by using
Ok, I will use no less then 35 and 280 for ecutwfc and ecutrho.
>> tot_charge = 0.000000,
>> starting_magnetization(1) = 0.0,
>> starting_magnetization(2) = 0.0,
>> starting_magnetization(3) = 0.0,
>> exxdiv_treatment = 'gygi-baldereschi' ,
>useless keywords (in this case...). Starting_magnetization(4) = x with
>0.0 < x < 1.0 is enough to
>break the spin symmetry.
>> nat = 33,
>The copper phthalocyanine (CuPc) has 57 atoms. Have you checked the
I calculate a _polymer_ of CuPc. The unit cell I've created contains 33
atoms, that should be correct.
>> ibrav = 6,
>> celldm(1) = 20.11677,
>> celldm(3) = 2.59367,
>your molecules embedded into a tetragonal cell seems to be placed at a
>z distance of about 30 A from
>its periodically repeated image... Check the exact use of the
Thank you! I was not careful in reading the manual and thought that
these parameters are just lengths of vectors.
>Molecular crystals stay together because of dispersion interactions.
>As you are not using any kind
>of dispersion correction, you will never obtain meaningful results on
>lattice parameters. There is
>plenty of theoretical papers investigating the CuPc molecule. I
>suggest to start with them...
Ok, thanks for pointing on that. Now I can play with calculations further.
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