fix sqm/out forces (#267)

* fix sqm/out forces

the output forces are actually gradients

* change float32 to float64

Author: njzjz

dpdata/amber/sqm.py

@@ -65,7 +65,7 @@ def parse_sqm_out(fname):
     data['coords'] = np.array([coords])
 
     energies = np.array(energies)
-    forces = np.array([forces], dtype=np.float32) * kcal2ev
+    forces = -np.array([forces], dtype=np.float64) * kcal2ev
     if len(forces) > 0:
         data['energies'] = energies
         data['forces'] = forces