diff --git a/docs/user_guide/4.2ADMPPmeForce.md b/docs/user_guide/4.2ADMPPmeForce.md
index 23fee795b..2353f4865 100644
--- a/docs/user_guide/4.2ADMPPmeForce.md
+++ b/docs/user_guide/4.2ADMPPmeForce.md
@@ -7,9 +7,9 @@ ADMPmeForce provides a support to multipolar polarizable electrostatic energy ca
 ### 1.1 Multipole Expansion
 
 The electrostatic interaction between two atoms can be described using multipole expansion, in which the electron cloud of an atom can be expanded as a series of multipole moments including charges, dipoles, quadrupoles, and octupoles etc. If only the charges (zero-moment) are considered, it is reduced to the point charge model in classical force fields:
-$$
+```math
 V=\sum_{ij} \frac{q_i q_j}{r_{ij}}
-$$
+```
 
 where $q_i$ is the charge of atom $i$.