diff --git a/lib/atc/ExtrinsicModelElectrostatic.cpp b/lib/atc/ExtrinsicModelElectrostatic.cpp
index c061b4184c..d876321baa 100644
--- a/lib/atc/ExtrinsicModelElectrostatic.cpp
+++ b/lib/atc/ExtrinsicModelElectrostatic.cpp
@@ -787,8 +787,7 @@ namespace ATC {
       xtArgs[3] = 1.; xtArgs[4] = 1.; xtArgs[5] = 1.;
       xtArgs[6] = coulombConstant*chargeDensity;
       xtArgs[7] = -1.;
-      string radialPower = "radial_power";
-      f = XT_Function_Mgr::instance()->function(radialPower,8,xtArgs);
+      f = XT_Function_Mgr::instance()->function("radial_power",8,xtArgs);
 
 
       for (iset = faceset->begin(); iset != faceset->end(); iset++) {
diff --git a/lib/atc/Function.cpp b/lib/atc/Function.cpp
index fb26cc0a18..0b228a9a41 100644
--- a/lib/atc/Function.cpp
+++ b/lib/atc/Function.cpp
@@ -48,7 +48,7 @@ namespace ATC {
   }
 
   // add user function into the if statement and assign returnFunction to it
-  UXT_Function* UXT_Function_Mgr::function(string & type, int nargs, double * args)
+  UXT_Function* UXT_Function_Mgr::function(const string & type, int nargs, double * args)
   {
     UXT_Function * returnFunction;
     if      (type=="linear") {
@@ -167,7 +167,7 @@ XT_Function_Mgr * XT_Function_Mgr::myInstance_ = nullptr;
   }
 
   // add user function into the if statement and assign returnFunction to it
-  XT_Function* XT_Function_Mgr::function(string & type, int nargs, double * args)
+  XT_Function* XT_Function_Mgr::function(const string & type, int nargs, double * args)
   {
     XT_Function * returnFunction;
     if      (type=="constant") {
diff --git a/lib/atc/Function.h b/lib/atc/Function.h
index 7c40cf6c54..448436adc4 100644
--- a/lib/atc/Function.h
+++ b/lib/atc/Function.h
@@ -110,7 +110,7 @@ namespace ATC {
     /** Static instance of this class */
     static UXT_Function_Mgr * instance();
 
-    UXT_Function* function(std::string & type, int nargs, double * arg);
+    UXT_Function* function(const std::string & type, int nargs, double * arg);
     UXT_Function* function(char ** arg, int nargs);
     UXT_Function* linear_function(double c0, double c1);
     UXT_Function* copy_UXT_function(UXT_Function* other);
@@ -181,7 +181,7 @@ namespace ATC {
     /** Static instance of this class */
     static XT_Function_Mgr * instance();
 
-    XT_Function* function(std::string & type, int nargs, double * arg);
+    XT_Function* function(const std::string & type, int nargs, double * arg);
     XT_Function* function(char ** arg, int nargs);
     XT_Function* constant_function(double c);
     XT_Function* copy_XT_function(XT_Function* other);