Plotting with two files [Reference]
If both files contain only one column, then the above command will print them one against the other.
plot "< join file1.dat file2.dat" u 1:2 w l
If both files have two columns, 1st column of file1.dat will be the x-axis and sum of 2nd columns of file1.dat and file2.dat will be the y-axis.
plot "< join file1.dat file2.dat" u 1:($2+$4) w l
Alternative
paste file1.dat file2.dat > file12.dat
===================================================================
set term postscript eps color enhanced
set output "ps_rho.eps"
set size 0.5,0.5
set xr[0:4]
set xlabel "r [Bohr]"
set ylabel "r^2{/Symbol r}"
p '< join core_correction density' u 1:($1*$1*($2+$6)) w l lw 2 t '{/Symbol r}_{v+c}',\
'density' u 1:($1*$1*$2) w l lw 2 t '{/Symbol r}_{v}' ,\
'core_correction' u 1:($1*$1*$2) w l lw 2 t '{/Symbol r}_{c}'
===============================================
file 'density' and "core_correction" are like
#
# Radial density.
# Length units: bohr
#
# -----------------------------------------------------------------------
# | r | n(r) | grad_n(r) | lapl_n(r) |
# -----------------------------------------------------------------------
3.74165729E-05 1.91929898E+03 -5.92105478E+05 -1.73335987E+10
3.83598792E-05 1.91874679E+03 -5.78741410E+05 -1.63009233E+10
3.93269671E-05 1.91819346E+03 -5.65711295E+05 -1.56454397E+10
4.03184362E-05 1.91763892E+03 -5.53006220E+05 -1.49307070E+10
4.13349012E-05 1.91708316E+03 -5.40618091E+05 -1.42734820E+10