diff --git a/doc/pair_zbl.html b/doc/pair_zbl.html
index 34635cb89c..26a583b33f 100644
--- a/doc/pair_zbl.html
+++ b/doc/pair_zbl.html
@@ -37,23 +37,19 @@ energy due to a pair of atoms at a distance r_ij is given by:
 </P>
 <CENTER><IMG SRC = "Eqs/pair_zbl.jpg">
 </CENTER>
-<P>where e is the electron
-charge, epsilon_0 is the electrical permittivity of vacuum, and 
-Z_i and Z_j are the nuclear charges of the two atoms in electron
-charge units. 
-The switching
-function S(r) is identical to that used by 
-<A HREF = "pair_gromacs.html">pair_style lj/gromacs</A>. 
-Here, the inner and outer cutoff are the same 
-for all pairs of atom types.
+<P>where e is the electron charge, epsilon_0 is the electrical
+permittivity of vacuum, and Z_i and Z_j are the nuclear charges of the
+two atoms.  The switching function S(r) is identical to that used by
+<A HREF = "pair_gromacs.html">pair_style lj/gromacs</A>.  Here, the inner and outer
+cutoff are the same for all pairs of atom types.
 </P>
 <P>The following coefficient must be defined for each pair of atom types
 via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples above,
-or in the LAMMPS data file. 
-Z can not be specified for two different atoms types.
-Therefore the lists of atom types I and atom types J must match.
+or in the LAMMPS data file.  Z can not be specified for two different
+atoms types.  Therefore the lists of atom types I and atom types J
+must match.
 </P>
-<UL><LI>Z (electron charge) 
+<UL><LI>Z (multiples of proton charge, e.g. 13.0 for aluminum) 
 </UL>
 <P>Although Z must be defined for all atom type pairs I,J, it is only
 stored for individual atom types, i.e. when I = J.  Z is normally equal
@@ -64,7 +60,8 @@ constants in the screening function depend on the unit of distance. In
 the above equation they are given for units of angstroms. LAMMPS will
 automatically convert these values to the distance unit of the
 specified LAMMPS <A HREF = "units.html">units</A> setting.  The values of Z should
-always be given in units of electron charge.
+always be given as multiples of a proton's charge, e.g. 29.0 for
+copper.
 </P>
 <HR>
 
diff --git a/doc/pair_zbl.txt b/doc/pair_zbl.txt
index b9c74a492b..a5256b6996 100644
--- a/doc/pair_zbl.txt
+++ b/doc/pair_zbl.txt
@@ -33,23 +33,19 @@ energy due to a pair of atoms at a distance r_ij is given by:
 
 :c,image(Eqs/pair_zbl.jpg)
 
-where e is the electron
-charge, epsilon_0 is the electrical permittivity of vacuum, and 
-Z_i and Z_j are the nuclear charges of the two atoms in electron
-charge units. 
-The switching
-function S(r) is identical to that used by 
-"pair_style lj/gromacs"_pair_gromacs.html. 
-Here, the inner and outer cutoff are the same 
-for all pairs of atom types.
+where e is the electron charge, epsilon_0 is the electrical
+permittivity of vacuum, and Z_i and Z_j are the nuclear charges of the
+two atoms.  The switching function S(r) is identical to that used by
+"pair_style lj/gromacs"_pair_gromacs.html.  Here, the inner and outer
+cutoff are the same for all pairs of atom types.
 
 The following coefficient must be defined for each pair of atom types
 via the "pair_coeff"_pair_coeff.html command as in the examples above,
-or in the LAMMPS data file. 
-Z can not be specified for two different atoms types.
-Therefore the lists of atom types I and atom types J must match.
+or in the LAMMPS data file.  Z can not be specified for two different
+atoms types.  Therefore the lists of atom types I and atom types J
+must match.
 
-Z (electron charge) :ul
+Z (multiples of proton charge, e.g. 13.0 for aluminum) :ul
 
 Although Z must be defined for all atom type pairs I,J, it is only
 stored for individual atom types, i.e. when I = J.  Z is normally equal
@@ -60,7 +56,8 @@ constants in the screening function depend on the unit of distance. In
 the above equation they are given for units of angstroms. LAMMPS will
 automatically convert these values to the distance unit of the
 specified LAMMPS "units"_units.html setting.  The values of Z should
-always be given in units of electron charge.
+always be given as multiples of a proton's charge, e.g. 29.0 for
+copper.
 
 :line
 
diff --git a/doc/units.html b/doc/units.html
index 73fc32ab2d..56a06790a8 100644
--- a/doc/units.html
+++ b/doc/units.html
@@ -75,7 +75,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = atmospheres
 <LI>dynamic viscosity = Poise
-<LI>charge = multiple of electron charge (+1.0 is a proton)
+<LI>charge = multiple of electron charge (1.0 is a proton)
 <LI>dipole = charge*Angstroms
 <LI>electric field = volts/Angstrom 
 <LI>density = gram/cm^dim 
@@ -92,7 +92,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = bars
 <LI>dynamic viscosity = Poise
-<LI>charge = multiple of electron charge (+1.0 is a proton)
+<LI>charge = multiple of electron charge (1.0 is a proton)
 <LI>dipole = charge*Angstroms
 <LI>electric field = volts/Angstrom
 <LI>density = gram/cm^dim 
@@ -109,7 +109,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = Pascals
 <LI>dynamic viscosity = Pascal*second
-<LI>charge = Coulombs
+<LI>charge = Coulombs (1.6021765e-19 is a proton)
 <LI>dipole = Coulombs*meters
 <LI>electric field = volts/meter 
 <LI>density = kilograms/meter^dim 
@@ -126,7 +126,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = dyne/cm^2 or barye = 1.0e-6 bars
 <LI>dynamic viscosity = Poise
-<LI>charge = statcoulombs or esu
+<LI>charge = statcoulombs or esu (4.8032044e-10 is a proton)
 <LI>dipole = statcoul-cm = 10^18 debye
 <LI>electric field = statvolt/cm or dyne/esu 
 <LI>density = grams/cm^dim 
@@ -141,7 +141,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>force = Hartrees/Bohr
 <LI>temperature = Kelvin
 <LI>pressure = Pascals
-<LI>charge = multiple of electron charge (+1.0 is a proton)
+<LI>charge = multiple of electron charge (1.0 is a proton)
 <LI>dipole moment = Debye
 <LI>electric field = volts/cm 
 </UL>
@@ -157,7 +157,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = picogram/(micrometer-microsecond^2)
 <LI>dynamic viscosity = picogram/(micrometer-microsecond)
-<LI>charge = picocoulombs
+<LI>charge = picocoulombs (1.6021765e-7 is a proton)
 <LI>dipole = picocoulomb-micrometer
 <LI>electric field = volt/micrometer 
 <LI>density = picograms/micrometer^dim 
@@ -174,7 +174,7 @@ by the number of atoms, i.e. energy/atom.  This can be changed via the
 <LI>temperature = Kelvin
 <LI>pressure = attogram/(nanometer-nanosecond^2)
 <LI>dynamic viscosity = attogram/(nanometer-nanosecond)
-<LI>charge = multiple of electron charge (+1.0 is a proton)
+<LI>charge = multiple of electron charge (1.0 is a proton)
 <LI>dipole = charge-nanometer
 <LI>electric field = volt/nanometer 
 <LI>density = attograms/nanometer^dim 
diff --git a/doc/units.txt b/doc/units.txt
index faf498d226..199d66ea26 100644
--- a/doc/units.txt
+++ b/doc/units.txt
@@ -72,7 +72,7 @@ torque = Kcal/mole
 temperature = Kelvin
 pressure = atmospheres
 dynamic viscosity = Poise
-charge = multiple of electron charge (+1.0 is a proton)
+charge = multiple of electron charge (1.0 is a proton)
 dipole = charge*Angstroms
 electric field = volts/Angstrom 
 density = gram/cm^dim :ul
@@ -89,7 +89,7 @@ torque = eV
 temperature = Kelvin
 pressure = bars
 dynamic viscosity = Poise
-charge = multiple of electron charge (+1.0 is a proton)
+charge = multiple of electron charge (1.0 is a proton)
 dipole = charge*Angstroms
 electric field = volts/Angstrom
 density = gram/cm^dim :ul
@@ -106,7 +106,7 @@ torque = Newton-meters
 temperature = Kelvin
 pressure = Pascals
 dynamic viscosity = Pascal*second
-charge = Coulombs
+charge = Coulombs (1.6021765e-19 is a proton)
 dipole = Coulombs*meters
 electric field = volts/meter 
 density = kilograms/meter^dim :ul
@@ -123,7 +123,7 @@ torque = dyne-centimeters
 temperature = Kelvin
 pressure = dyne/cm^2 or barye = 1.0e-6 bars
 dynamic viscosity = Poise
-charge = statcoulombs or esu
+charge = statcoulombs or esu (4.8032044e-10 is a proton)
 dipole = statcoul-cm = 10^18 debye
 electric field = statvolt/cm or dyne/esu 
 density = grams/cm^dim :ul
@@ -138,7 +138,7 @@ velocity = Bohr/atomic time units \[1.03275e-15 seconds\]
 force = Hartrees/Bohr
 temperature = Kelvin
 pressure = Pascals
-charge = multiple of electron charge (+1.0 is a proton)
+charge = multiple of electron charge (1.0 is a proton)
 dipole moment = Debye
 electric field = volts/cm :ul
 
@@ -154,7 +154,7 @@ torque = picogram-micrometer^2/microsecond^2
 temperature = Kelvin
 pressure = picogram/(micrometer-microsecond^2)
 dynamic viscosity = picogram/(micrometer-microsecond)
-charge = picocoulombs
+charge = picocoulombs (1.6021765e-7 is a proton)
 dipole = picocoulomb-micrometer
 electric field = volt/micrometer 
 density = picograms/micrometer^dim :ul
@@ -171,7 +171,7 @@ torque = attogram-nanometer^2/nanosecond^2
 temperature = Kelvin
 pressure = attogram/(nanometer-nanosecond^2)
 dynamic viscosity = attogram/(nanometer-nanosecond)
-charge = multiple of electron charge (+1.0 is a proton)
+charge = multiple of electron charge (1.0 is a proton)
 dipole = charge-nanometer
 electric field = volt/nanometer 
 density = attograms/nanometer^dim :ul