diff --git a/pysimm/amber.py b/pysimm/amber.py
index 7b5f77a..e4a206c 100644
--- a/pysimm/amber.py
+++ b/pysimm/amber.py
@@ -63,10 +63,10 @@ def cleanup_antechamber():
             print('problem removing {} during cleanup'.format(fname))
 
 
-def calc_charges(s, charge_method='bcc', cleanup=True):
+def calc_charges(s, charge_method='bcc', net_charge='0', cleanup=True):
     """pysimm.amber.calc_charges
 
-    Calculates charges using antechamber. Defaults to am1-bcc charges. 
+    Calculates charges using antechamber. Defaults to am1-bcc charges and neutral charge. 
 
     Args:
         s: System for which to calculate charges. System object is updated in place
@@ -77,7 +77,7 @@ def calc_charges(s, charge_method='bcc', cleanup=True):
         None
     """
     s.write_pdb('pysimm.tmp.pdb')
-    cl = '{} -fi pdb -i pysimm.tmp.pdb -fo ac -o pysimm.tmp.ac -c {}'.format(ANTECHAMBER_EXEC, charge_method)
+    cl = '{} -fi pdb -i pysimm.tmp.pdb -fo ac -o pysimm.tmp.ac -c {} -nc {}'.format(ANTECHAMBER_EXEC, charge_method, net_charge)
     p = Popen(cl.split(), stdin=PIPE, stdout=PIPE, stderr=PIPE)
     p.communicate()
     with file('pysimm.tmp.ac') as f:
diff --git a/pysimm/forcefield/dreiding.py b/pysimm/forcefield/dreiding.py
index 3c53de9..eb302f1 100644
--- a/pysimm/forcefield/dreiding.py
+++ b/pysimm/forcefield/dreiding.py
@@ -86,7 +86,11 @@ def assign_ptypes(self, s):
                 p.nbonds += 1
         for p in s.particles:
             if p.elem == 'H':
-                p.type_name = 'H_'
+                for pb in p.bonded_to:
+                    if pb.elem == 'O' or pb.elem == 'N':
+                        p.type_name = 'H___A'
+                if not p.type_name:
+                    p.type_name = 'H_'
             elif p.elem == 'C':
                 if p.bond_orders and (4 in p.bond_orders or 'A' in p.bond_orders):
                     p.type_name = 'C_R'
@@ -357,4 +361,4 @@ def assign_charges(self, s, charges='gasteiger'):
         """
         if charges == 'gasteiger':
             print('adding gasteiger charges')
-            gasteiger.set_charges(s)
\ No newline at end of file
+            gasteiger.set_charges(s)