fix typos in doc

doc/nep/input_parameters/use_typewise_cutoff.rst

@@ -1,18 +1,18 @@
-.. _kw_cutoff:
+.. _kw_use_typewise_cutoff:
 .. index::
  single: use_typewise_cutoff (keyword in nep.in)
 
 :attr:`use_typewise_cutoff`
 ===========================
 
-This keyword enables one to use typewise cutoff radii for the radial (:math:`r_\mathrm{c}^\mathrm{R}`) and angular (:math:`r_\mathrm{c}^\mathrm{A}`) descriptors of the :term:`NEP` model.
+This keyword enables one to use typewise cutoff radii for the radial and angular descriptors of the :term:`NEP` model.
 The syntax is::
 
  use_typewise_cutoff
 
 without any parameter.
 
-If this keyword is present, the radial cutoff between elements I and J is the minimum between the global radial cutoff :math:`r_\mathrm{c}^\mathrm{R}` and 2.5 times of the sum of the covalent radii of the two elements, and the angular cutoff between elements I and J is the minimum between the global angular cutoff :math:`r_\mathrm{c}^\mathrm{R}` and 2.0 times of the sum of the covalent radii of the two elements.
+If this keyword is present, the radial cutoff between two elements is the minimum between the global radial cutoff :math:`r_\mathrm{c}^\mathrm{R}` and 2.5 times of the sum of the covalent radii of the two elements, and the angular cutoff between two elements is the minimum between the global angular cutoff :math:`r_\mathrm{c}^\mathrm{A}` and 2.0 times of the sum of the covalent radii of the two elements.
 
 By default, this keyword is not in effect.
 

doc/nep/input_parameters/use_typewise_cutoff_zbl.rst

@@ -1,4 +1,4 @@
-.. _kw_cutoff:
+.. _kw_use_typewise_cutoff_zbl:
 .. index::
  single: use_typewise_cutoff_zbl (keyword in nep.in)
 
@@ -12,6 +12,6 @@ The syntax is::
 
 without any parameter.
 
-If this keyword is present, the outer ZBL cutoff between elements I and J is the minimum between the global ZBL outer cutoff :math:`r_\mathrm{outer}^\mathrm{ZBL}` and 0.6 times of the sum of the covalent radii of the two elements, and the inner ZBL cutoff is half of the outer one.
+If this keyword is present, the outer ZBL cutoff between two elements is the minimum between the global outer ZBL cutoff :math:`r_\mathrm{outer}^\mathrm{ZBL}` and 0.6 times of the sum of the covalent radii of the two elements, and the inner ZBL cutoff is half of the outer one.
 
 By default, this keyword is not in effect.