force-field.md

@@ -258,15 +258,15 @@ When molecular species are defined, additional intramolecular terms are included
 
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-Different water models have been developped which introduce a fourth virtual atom. This dummy atom is placed at a given distance $`d`$ from the oxygen atom O, on the bisector of the H-O-H angle. In these models, such as TIP4P or Dang-Chang water model, the charge and/or polarizability of the oxygen atom is placed on the dummy atom. 
+Different water models have been developped which introduce a fourth virtual atom M. This dummy atom is placed at a given distance $`d`$ from the oxygen atom O, on the bisector of the H-O-H angle. In these models, such as TIP4P or Dang-Chang water model, the charge and/or polarizability of the oxygen atom is placed on the dummy atom M. 
 The implementation in MW requires the definition of the dummy atom and redistributes the force on the dummy atom on the hydrogen and oxygen atoms, as described in [[Feenstra1999][6]].
 These models are usually used with RATTLE constraints to fix the O-H bonds and the H-O-H angle.
 
 The stress tensor calculation is done by redistributing the stress on the virtual atom onto the hydrogen and oxygen atoms as
 ```math
-S = S - \vec{OM} \times \vec{F}_{O} - \vec{H_1 M} \times \vec{F}_{H_1} - \vec{H_2 M} \times \vec{F}_{H_2}
+S_{ij} = S_{ij} - r_i^{OM}  F_j^{O} - r_i^{H_1M}  F_j^{H_1} - r_i^{H_2M}  F_j^{H_2}
 ```
-where $`\vec{F}_X`$ is the redistributed force on atom X. 
+where $`F_j^X`$ is the $`j`$ components of the redistributed force on atom X and $`r_i^XM`$ is the $`i`$ component of the $`\vec{XM}`$ vector.