Fix typos referencing D4 instead of D3 (#152)

Author: awvwgk

python/README.rst

@@ -110,7 +110,7 @@ For convenience ``DFTD3`` allows to combine itself with another calculator by us
 
    >>> from ase.build import molecule
    >>> from ase.calculators.emt import EMT
-   >>> from dftd4.ase import DFTD3
+   >>> from dftd3.ase import DFTD3
    >>> atoms = molecule("C60")
    >>> atoms.calc = DFTD3(method="pbe", damping="d3bj").add_calculator(EMT())
    >>> atoms.get_potential_energy()

python/dftd3/pyscf.py

@@ -192,7 +192,7 @@ def kernel(self) -> Tuple[float, np.ndarray]:
         Returns
         -------
         float, ndarray
-            The energy and gradient of the DFT-D4 dispersion correction.
+            The energy and gradient of the DFT-D3 dispersion correction.
 
         Examples
         --------
@@ -207,8 +207,8 @@ def kernel(self) -> Tuple[float, np.ndarray]:
         ...          H     0.000000    0.000000   -5.444276
         ...          '''
         ... )
-        >>> d4 = disp.DFTD3Dispersion(mol, xc="PBE0")
-        >>> energy, gradient = d4.kernel()
+        >>> d3 = disp.DFTD3Dispersion(mol, xc="PBE0")
+        >>> energy, gradient = d3.kernel()
         >>> energy
         array(-0.00303589)
         >>> gradient

python/dftd3/test_ase.py

@@ -36,7 +36,7 @@ def get_calcs(calc) -> Iterator[ase.calculators.calculator.Calculator]:
 
 
 @pytest.mark.skipif(ase is None, reason="requires ase")
-def test_ase_scand4():
+def test_ase_scand3():
     thr = 1.0e-6
 
     forces = np.array(
@@ -67,7 +67,7 @@ def test_ase_scand4():
 
 
 @pytest.mark.skipif(ase is None, reason="requires ase")
-def test_ase_tpssd4():
+def test_ase_tpssd3():
     thr = 1.0e-6
 
     forces = np.array(