[Pw_forum] Point Charges for Molecular Dynamics

[Kevin Schmidt]

Hello PWSCF Forum,

First time caller, long time listener.  I am working with a group using
Quantum Espresso to extract two-body interatomic potentials (IP) for an
ionic crystal system (metal borides, to be exact).  These potentials will
then be put to use in molecular dynamics software (DL-Poly).  From my
understanding with MD, most software nowadays typically employs
electrostatics as a separate potential from the heteronuclear IP's.  In
order to (1) get the correct heteronuclear IP and (2) simulate a
"realistic" electrostatic environment in MD, it would be best to have the
right point charges for the system.  After browsing through the forum and
user guides, I noticed that PP.x (plot_num = 0) has the ability to output
charge density distributions.  The output I received had, depending on
which plot type used, five or six columns, of which I am assuming are
related to charge values on a grid.  Is this correct, and if so, how do I
find the corresponding grid?

My idea was to integrate the charge density in a Wigner-Seitz cell around
each ion to get point charges for use in electrostatics.  I'm not sure if
there's a better way to accomplish this goal; this was my attempt.  I
apologize if I have overlooked a thread, please notify me so.  Thanks in
advance and I look forward to your advice.

P.S.  The output I received for a model system is given below for a
specified "filplot", plot_num = 0.


      72      72      72      72      72      72       4       2
     1        7.00000000      0.00000000      0.00000000      0.00000000
   0.00000000      0.00000000
     1191.5371196339       12.0000000000       80.0000000000     0
   1   La   11.00
   2   B     3.00
   1       0.000000000    0.000000000    0.000000000    1
   2       0.000000000    0.500000000    0.500000000    2
   3       0.500000000    0.000000000    0.500000000    2
   4       0.500000000    0.500000000    0.000000000    2
  3.434814311E-01  3.431749032E-01  3.422272391E-01  3.405249826E-01
 3.378906730E-01
  3.341004832E-01  3.288993448E-01  3.220354913E-01  3.132873382E-01
 3.024951442E-01
  2.895821234E-01  2.745777240E-01  2.576219405E-01  2.389737928E-01
 2.190001080E-01
  1.981636489E-01  1.769910061E-01  1.560378501E-01  1.358452121E-01
 1.168975755E-01
  9.959052347E-02  8.420256729E-02  7.088392771E-02  5.965905586E-02
 5.043519819E-02
..... more values

-- 
Kevin Schmidt
*Chemical Engineering Department*
*University of Nevada, Reno, USA*
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