Can't output the surface potential correctly

[Yongqiang]

Hi All,

I try to modify the example 8 by adding the cd-music model. But when try to plot the potential at different surfaces, I encounter some problems. All the potential turn out to be 0. Anyone have some knowledge on how to find the problem?

Thanks a lot.
Yongqiang

Code: [Select]

TITLE Example 8.--Sorption of zinc on hydrous iron oxides.
SURFACE_SPECIES
     Hfo_sOH  + H+ = Hfo_sOH2+
     log_k  7.18
     Hfo_sOH = Hfo_sO- + H+
     log_k  -8.82
     Hfo_sOH + Zn+2 = Hfo_sOZn+ + H+
     log_k  0.66
     Hfo_wOH  + H+ = Hfo_wOH2+
     log_k  7.18
     Hfo_wOH = Hfo_wO- + H+
     log_k  -8.82
     Hfo_wOH + Zn+2 = Hfo_wOZn+ + H+
     log_k  -2.32
SURFACE 1
     -cd_music
     Hfo_sOH        5e-6    600.    0.09
     Hfo_wOH        2e-4
     -capacitance 0.98 0.73
#     -donnan
END
SOLUTION 1
     -units  mmol/kgw
     pH      8.0
     Zn      0.0001
     Na      100.    charge
     N(5)    100.
SELECTED_OUTPUT
     -file Zn1e_7
     -reset false
USER_PUNCH
  10 FOR i = 5 to 8 STEP 0.25
  20 a$ = EOL$ + "USE solution 1" + CHR$(59) + " USE surface 1" + EOL$
  30 a$ = a$ + "EQUILIBRIUM_PHASES 1" + EOL$
  40 a$ = a$ + "   Fix_H+ " + STR$(-i) + " NaOH 10.0" + EOL$
  50 a$ = a$ + "END" + EOL$
  60 PUNCH a$
  70 NEXT i
END
SOLUTION 2
     -units  mmol/kgw
     pH      8.0
     Zn      0.1
     Na      100.    charge
     N(5)    100.
SELECTED_OUTPUT
     -file Zn1e_4
     -reset false
USER_PUNCH
  10 FOR i = 5 to 8 STEP 0.25
  20 a$ = EOL$ + "USE solution 2" + CHR$(59) + " USE surface 1" + EOL$
  30 a$ = a$ + "EQUILIBRIUM_PHASES 1" + EOL$
  40 a$ = a$ + "   Fix_H+ " + STR$(-i) + " NaOH 10.0" + EOL$
  50 a$ = a$ + "END" + EOL$
  60 PUNCH a$
  70 NEXT i
END
#
# Model definitions
#
PHASES
     Fix_H+
     H+ = H+
     log_k  0.0
END
#
#   Zn = 1e-7
SELECTED_OUTPUT
     -file ex8.sel
     -reset true
     -molalities     Zn+2    Hfo_wOZn+      Hfo_sOZn+
USER_PUNCH
 10
USER_GRAPH 1 Example 8
     -headings pH 0plane 1plane 2plane
     -chart_title "Potential Zn = 1e-7 molal"
     -axis_titles pH "MOLES PER KILOGRAM WATER" "CHARGE BALANCE, IN MILLIEQUIVALENTS"
     -axis_scale x_axis auto
     -axis_scale y_axis auto
     #-axis_scale sy_axis -0.15 0 0.03
  -start
  10 GRAPH_X -LA("H+")
  20 GRAPH_Y EDL("psi","Hfo"),EDL("psi1","Hfo"),EDL("psi2","Hfo")#MOL("Zn+2"), MOL("Hfo_wOZn+"), MOL("Hfo_sOZn+")
  #30 GRAPH_SY CHARGE_BALANCE * 1e3
  -end
INCLUDE$ Zn1e_7
END
USER_GRAPH 1
     -detach
END
#
#   Zn = 1e-4
USER_GRAPH 2 Example 8
     -chart_title "Total Zn = 1e-4 molal"
     -headings pH Zn_solute Zn_weak_sites Zn_strong_sites Charge_Balance
     -axis_titles pH "MOLES PER KILOGRAM WATER" "CHARGE BALANCE, IN MILLIEQUIVALENTS"
     -axis_scale x_axis auto
     -axis_scale y_axis auto
     #-axis_scale sy_axis -0.15 0 0.03
  -start
  10 GRAPH_X -LA("H+")
  20 GRAPH_Y EDL("psi","Hfo"),EDL("psi1","Hfo"),EDL("psi2","Hfo")
  #30 GRAPH_SY CHARGE_BALANCE * 1e3
  -end       
INCLUDE$ Zn1e_4
END

[dlparkhurst]

You must define the surface species to be -cd_music species. Attached is a cd_music example for goethite sorption, and it relies on many references by Hiemstra and colleagues to parameterize the sites on the surface of goethite. Your definitions lack the -cd_music definition in SURFACE_SPECIES and are not based on a thorough parameterization of a surface using the cd_music theory.

[Yongqiang]

Hi David,

I can't thank you more. It really helps me out!

Best Regards,
Yongqiang