add example

.gitignore

@@ -0,0 +1,11 @@
+#example/**
+*.pyc
+src/__pycache__/**
+example.tar
+*.hdf5
+*.h5
+*WFN*
+*WFNq*
+*.upf
+*.dat
+*.npy

README.md

@@ -2,7 +2,24 @@
 Directory for Libxc totorial
 
 We have following example systems
+
     1. Graphene: metalic system with occupation smearing
-    2. WSe2    : insulating system w/o occupation smearing
+    2. WS2     : insulating system w/o occupation smearing
+
+For each example system, we have LDA/GGA example directries.
+
+In each directory, we compute
+
+    1. Vxc(r) and  <mk|Vxc|nk> from pw2bgw.x ... Ref
+    2. Vxc(r) and  <mk|Vxc|nk> from pp.x
+    3. Vxc(r) and  <mk|Vxc|nk> from Libxc
 
 We only consider collinear calculation.
+
+
+For method 2.
+
+    we first do pp.x and print Vxc(r) = Vtot(r) - Vbare(r) - Vhatree(r) in a FFTgrid and then
+        
+    1-1. do FFT Vxc(r) to Vxc(g). Then we can compute <mk|Vxc|nk> in G-space.
+    1-2. do IFFT unk(g) to unk(r). Then we can compute <mk|Vxc|nk> in R-space.

WS2/GGA/1-scf/scf.in

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+&control
+   prefix = 'WS2'
+   pseudo_dir = '/global/u2/w/wkim94/pseudo/pseudodojo/nc-sr-04_pbe_standard_upf/'
+   !pseudo_dir = '/work2/08702/wkim94/frontera/pseudo/pseudodojo/nc-sr-04_pbe_standard_upf/'
+   calculation = 'scf'
+   verbosity = 'high'
+/
+&system
+   ecutwfc = 20.0
+!   A = 3.290
+   ibrav = 0
+   nat = 3
+   ntyp = 2
+!   lspinorb = .true.
+!   noncolin = .true.
+   nosym = .true.
+   noinv = .true.
+/
+&electrons
+   electron_maxstep = 100
+   conv_thr = 1e-06
+   mixing_mode = 'plain'
+   mixing_beta = 0.3
+   mixing_ndim = 8
+   diagonalization = 'david'
+   diago_david_ndim = 4
+   diago_full_acc = .true.
+/
+CELL_PARAMETERS {angstrom}
+3.1500000000000 0.000000000000  0.00
+1.575000000000  2.7279800219    0.00 
+0.000000000000  0.000000000000  25.0 
+ATOMIC_SPECIES 
+   W 183.84 'W.upf'
+   S 78.96  'S.upf'
+ATOMIC_POSITIONS crystal
+ W   0.33333333333333 0.33333333333333 0.5000000000 
+ S   0.66666666666667 0.66666666666667 0.4360000000 
+ S   0.66666666666667 0.66666666666667 0.5640000000 
+K_POINTS automatic
+6 6 1 0 0 0