[Tests] Add test for small cell

tests/06_SDFT/24_PW_SDFT_SMALL_CELL/INPUT

@@ -0,0 +1,35 @@
+INPUT_PARAMETERS
+#Parameters (1.General)
+suffix          autotest
+calculation     scf
+esolver_type    sdft
+symmetry        1
+pseudo_dir      ../../PP_ORB
+orbital_dir     .
+basis_type      pw
+ecutwfc         500
+cal_stress      1
+cal_force       1
+kpar            1
+bndpar          1
+
+#Parameters (2. SCF iterations)
+scf_thr         1e-6
+
+#Parameters (3. Solve KS equation)
+nbands          0
+nbands_sto      96
+nche_sto        50
+seed_sto        20000
+pw_seed         1
+method_sto      2
+ks_solver       cg
+
+#Parameters (4.Smearing)
+smearing_method     fd
+smearing_sigma      25.33454852
+
+#Parameters (5.Mixing)
+mixing_type     broyden
+mixing_beta     0.7
+mixing_gg0      0

tests/06_SDFT/24_PW_SDFT_SMALL_CELL/KPT

@@ -0,0 +1,4 @@
+K_POINTS
+0
+Gamma
+2 1 1 0 0 0

tests/06_SDFT/24_PW_SDFT_SMALL_CELL/README

@@ -0,0 +1 @@
+test SDFT SCF correctness on a very small cell with lightweight settings

tests/06_SDFT/24_PW_SDFT_SMALL_CELL/STRU

@@ -0,0 +1,23 @@
+#This is the atom file containing all the information
+#about the lattice structure.
+
+ATOMIC_SPECIES
+D 2.0141017778 H.SG15.PBE.UPF	#Element, Mass, Pseudopotential
+
+LATTICE_CONSTANT
+0.3838341862  			#Lattice constant
+
+LATTICE_VECTORS
+1.0 0.0 0.0 		#Lattice vector 1
+0.0 1.0 0.0		    #Lattice vector 2
+0.0 0.0 1.0 		#Lattice vector 3
+
+ATOMIC_POSITIONS
+Direct
+D			#Name of element
+0.0
+4
+0.000   0.000   0.000   1       1       1
+0.000   0.500   0.500   1       1       1
+0.500   0.000   0.500   1       1       1
+0.500   0.500   0.000   1       1       1

tests/06_SDFT/24_PW_SDFT_SMALL_CELL/result.ref

@@ -0,0 +1,8 @@
+etotref 3259.2802240676614929
+etotperatomref 814.8200560169
+totalforceref 0.000000
+totalstressref 1271683315.068934
+pointgroupref O_h
+spacegroupref O_h
+nksibzref 2
+totaltimeref 3.01

tests/06_SDFT/CASES_CPU.txt

@@ -21,3 +21,4 @@
 21_PW_SKG_10D10S
 22_PW_SKG_ALL
 23_PW_SNLKG_10D10S
+24_PW_SDFT_SMALL_CELL