Added regression test for KKRnano using constraining magnetism.

A simple two-atom bcc Fe unit cell, constraint to some
non-groundstate configuration. Also uses external fields.

Note that the new test case needs two iterations so that the
updated constraining field effects the calculation and thus this
update is checked.

source/KKRnano/regtests/Fe/bfield.dat

+# theta [deg], phi [deg], strenght [Ry]
+         30.0        0.0         4.0e-3
+         30.0        0.0         4.0e-3

source/KKRnano/regtests/Fe/input.conf

+# bcc Fe, constrained magnetic configuration
+
+# LATTICE
+alat       = 5.423
+
+bravais_a =  1.0   0.0   0.0
+bravais_b =  0.0   1.0   0.0
+bravais_c =  0.0   0.0   1.0
+
+cartesian = t
+
+
+# PHYSICS
+kxc    = 2
+nsra   = 2     # on
+NSPIND = 2
+KORBIT = 1
+soc    = t
+
+# MAGNETIC FIELDS
+noncobfield = t
+external_bfield = t
+mt_bfield = t
+constr_bfield_mixing = 1.0
+bfield_verbosity = 3
+
+
+# SELF-CONSISTENCY OPTIONS
+scfsteps =   2
+imix     =   1
+mixing   =   0.1
+fcm      =  20.0
+target_rms = 1.0d-8
+
+
+# ENERGY CONTOUR
+emin  =  -0.5
+emax  =   1.5
+npnt1 =   3
+npnt2 =   6
+npnt3 =   3
+npol  =   3
+tempr = 800.0
+
+
+# SOLVER
+bzdivide  =  4  4  4
+
+
+# PARAMETERS FOR EWALD SUMS
+rmax = 6.d0
+gmax = 65.d0
+
+
+# SHAPE-FUNCTION OPTIONS
+rclust_voronoi = 1.8
+r_log = 0.8
+
+
+# OUTPUT
+kte          = 1
+kforce       = 1

source/KKRnano/regtests/Fe/nonco_angle.dat

+  0.000000000000000E+000  0.000000000000000E+000    2
+   60.0000000000000       0.000000000000000E+000    2

source/KKRnano/regtests/Fe/rbasis.xyz

+2
+Fe bcc
+Fe    0.0  0.0  0.0
+Fe    0.5  0.5  0.5

source/KKRnano/regtests/tests.py

@@ -21,6 +21,7 @@ ShowMD5 = True
 AllMPIs = 1 # 1=Yes, 0=No
 HighLmax = True
 testNocoSOC = True
+testBconstr = True
 verbose = False
 MPIEXEC = 'mpirun' # 'srun'
 
@@ -178,5 +179,13 @@ class Test_nocosocmaterials(unittest.TestCase):
             self.assertAlmostEqual(KKRnano("MnGeB20", solver=iterative, nranks=4), Etot, DECIMALS) # takes longer than other tests
         # total time ~6min
 
+class Test_constrainedmagnetism(unittest.TestCase):
+    def test_bcc_Fe(self):
+        """Test two-atom bcc Fe unit cell constrained to a 60 degree angle"""
+        Etot = -5082.33743334
+        if testBconstr:
+            self.assertAlmostEqual(KKRnano("Fe", solver=direct, nranks=2), Etot, DECIMALS)
+        # About 6min (Needs two iterations so that updated constraining fields are used.)
+
 
 unittest.main()