add example

Signed-off-by: Jinzhe Zeng <[email protected]>

doc/model/dpa2.md

@@ -26,6 +26,8 @@ When using the JAX backend, 2 or more MPI ranks are not supported. One must set
 atom_modify map yes
 ```
 
+See the example `examples/water/lmp/jax_dpa2.lammps`.
+
 ## Data format
 
 DPA-2 supports both the [standard data format](../data/system.md) and the [mixed type data format](../data/system.md#mixed-type).

examples/water/lmp/jax_dpa2.lammps

@@ -0,0 +1,31 @@
+
+
+# bulk water
+
+units           metal
+boundary        p p p
+atom_style      atomic
+# Below line is required when using DPA-2 with the JAX backend
+atom_modify     map yes
+
+neighbor        2.0 bin
+neigh_modify    every 10 delay 0 check no
+
+read_data	water.lmp
+mass 		1 16
+mass		2 2
+
+# See https://deepmd.rtfd.io/lammps/ for usage
+pair_style	deepmd frozen_model.savedmodel
+# If atom names (O H in this example) are not set in the pair_coeff command, the type_map defined by the training parameter will be used by default.
+pair_coeff  * *	O H
+
+velocity        all create 330.0 23456789
+
+fix             1 all nvt temp 330.0 330.0 0.5
+timestep        0.0005
+thermo_style    custom step pe ke etotal temp press vol
+thermo          100
+dump		1 all custom 100 water.dump id type x y z
+
+run             1000