Fixed a few features with phases consisting solely of electrons.

Cantera/src/equil/vcs_MultiPhaseEquil.cpp

@@ -1036,6 +1036,9 @@ namespace VCSnonideal {
        * Also decide whether we need a new charge neutrality
        * element in the phase to enforce a charge neutrality
        * constraint.
+       *  We also decide whether this is a single species phase
+       *  with the voltage being the independent variable setting
+       *  the chemical potential of the electrons.
        */
       VolPhase->transferElementsFM(tPhase);
 
@@ -1338,11 +1341,14 @@ namespace VCSnonideal {
 	vprob->w[kglob] = tPhase->electricPotential();
       }
       volPhase->setMolesFromVCS(VCS_STATECALC_OLD, VCS_DATA_PTR(vprob->w));
-      if (volPhase->totalMoles() > 0.0) {
-	volPhase->setExistence(1);
+      if ((nSpPhase == 1) && (volPhase->phiVarIndex() == 0)) {
+	volPhase->setExistence(VCS_PHASE_EXIST_ALWAYS);
+      }	else if (volPhase->totalMoles() > 0.0) {
+	volPhase->setExistence(VCS_PHASE_EXIST_YES);
       } else {
-	volPhase->setExistence(0);
+	volPhase->setExistence(VCS_PHASE_EXIST_NO);
       }
+   
     }
     /*
      *  Transfer initial element abundances to the vprob object.

Cantera/src/equil/vcs_VolPhase.cpp

@@ -51,6 +51,7 @@ namespace VCSnonideal {
     m_useCanteraCalls(false),
     TP_ptr(0),
     v_totalMoles(0.0),
+    m_phiVarIndex(-1),
     m_totalVol(0.0),
     m_vcsStateStatus(VCS_STATECALC_OLD),
     m_phi(0.0),
@@ -1189,11 +1190,15 @@ namespace VCSnonideal {
       }
 #endif
     } else {
+      if (m_singleSpecies && (m_phiVarIndex == 0)) {
+	m_existence =  VCS_PHASE_EXIST_ALWAYS;
+      } else {
       if (totalMols > 0.0) {
 	m_existence = VCS_PHASE_EXIST_YES;
       } else {
 	m_existence = VCS_PHASE_EXIST_NO;
       }
+      }
     }
   }
   /***************************************************************************/
@@ -1284,6 +1289,12 @@ namespace VCSnonideal {
 
   void vcs_VolPhase::setPhiVarIndex(int phiVarIndex) {
     m_phiVarIndex = phiVarIndex;
+    m_speciesUnknownType[m_phiVarIndex] = VCS_SPECIES_TYPE_INTERFACIALVOLTAGE;
+    if (m_singleSpecies) {
+      if (m_phiVarIndex == 0) {
+	m_existence = VCS_PHASE_EXIST_ALWAYS;
+      }
+    }
   }
   /***************************************************************************/
 
@@ -1320,7 +1331,20 @@ namespace VCSnonideal {
     else { 
       if (m_totalMolesInert == 0.0) {
 	if (v_totalMoles == 0.0) {
-	  plogf("vcs_VolPhase::setExistence setting true existence for phase with no moles");
+	  if (!m_singleSpecies  || m_phiVarIndex != 0) {
+	    plogf("vcs_VolPhase::setExistence setting true existence for phase with no moles");
+	    plogendl();
+	    exit(EXIT_FAILURE);
+	  }
+	}
+      }
+    }
+#endif
+#ifdef DEBUG_MODE
+    if (m_singleSpecies) {
+      if (m_phiVarIndex == 0) {
+	if (existence == VCS_PHASE_EXIST_NO || existence == VCS_PHASE_EXIST_ZEROEDPHASE) {
+	  plogf("vcs_VolPhase::Trying to set existence of an electron phase to false");
 	  plogendl();
 	  exit(EXIT_FAILURE);
 	}
@@ -1376,6 +1400,8 @@ namespace VCSnonideal {
     }
     if (m_totalMolesInert > 0.0) {
       m_existence = VCS_PHASE_EXIST_ALWAYS;
+    } else if (m_singleSpecies && (m_phiVarIndex == 0)) {
+      m_existence = VCS_PHASE_EXIST_ALWAYS;
     } else {
       if (v_totalMoles > 0.0) {
 	m_existence = VCS_PHASE_EXIST_YES;

Cantera/src/equil/vcs_VolPhase.h

@@ -176,7 +176,8 @@ namespace VCSnonideal {
      *  then updates this object with their values. This is essentially
      *  a gather routine.
      *
-     *  @param molesSpeciesVCS  array of mole numbers. Note, the indecises for species in 
+     *  @param molesSpeciesVCS  Array of mole numbers. Note, the indecises
+     *            for species in 
      *            this array may not be contiguous. IndSpecies[] is needed
      *            to gather the species into the local contiguous vector
      *            format. 
@@ -434,6 +435,8 @@ namespace VCSnonideal {
     //! Returns whether the object is using cantera calls.
     bool usingCanteraCalls() const;
 
+    //! Return the index of the species that represents the 
+    //! the voltage of the phase
     int phiVarIndex() const;
 
     void setPhiVarIndex(int phiVarIndex);
@@ -465,7 +468,7 @@ namespace VCSnonideal {
      *  @param spIndex local species index (0 to the number of species
      *                 in the phase)
      *
-     * @return Returns the VCS_SOLVE species index of the that species
+     * @return Returns the VCS_SOLVE species index of the species.
      *         This changes as rearrangements are carried out. 
      */
     int spGlobalIndexVCS(const int spIndex) const;
@@ -794,15 +797,19 @@ namespace VCSnonideal {
 
     //! Current state of existence:
     /*!
-     *     VCS_PHASE_EXIST_ZEROEDPHASE = -6: Set to not exist by fiat from a higher level.
+     *     VCS_PHASE_EXIST_ZEROEDPHASE = -6: Set to not exist by fiat from a 
+     *          higher level.
      *          This is used in phase stability boundary calculations
      *     VCS_PHASE_EXIST_NO = 0:   Doesn't exist currently
-     *     VCS_PHASE_EXIST_MINORCONC = 1:  Exists, but the concentration is so low that an alternate
+     *     VCS_PHASE_EXIST_MINORCONC = 1:  Exists, but the concentration is 
+     *          so low that an alternate
      *          method is used to calculate the total phase concentrations.
      *     VCS_PHASE_EXIST_YES = 2 : Does exist currently
      *     VCS_PHASE_EXIST_ALWAYS = 3: Always exists because it contains
-     *          inerts which can't exist in any other
-     *          phase  
+     *          inerts which can't exist in any other phase. Or,
+     *          the phase exists always because it consists of a single
+     *          species, which is identified with the voltage, i.e., 
+     *          its an electron metal phase.
      */
     int m_existence;