Mix eta in Electrode package

doc/src/fix_electrode.rst

@@ -70,6 +70,8 @@ Syntax
         filename = file from which to read inverted matrix
     *qtotal* value = number or *v_* equal-style variable
         add overall potential so that all electrode charges add up to *qtotal*
+    *eta* value = d_propname
+        d_propname = a custom double vector defined via fix property/atom
 
 Examples
 """"""""
@@ -264,6 +266,11 @@ individual electrodes, and since *symm on* constrains the total charge of all
 electrodes to be zero, either option is incompatible with the *qtotal* keyword
 (even if *qtotal* is set to zero).
 
+The keyword *eta* takes the name of a custom double vector defined via fix
+property/atom.  The values will be used instead of the standard eta value.  The
+property/atom fix must be for vector of double values and use the *ghost on*
+option.
+
 Restart, fix_modify, output, run start/stop, minimize info
 """""""""""""""""""""""""""""""""""""""""""""""""""""""""""
 

examples/PACKAGES/electrode/madelung/data.eta

@@ -0,0 +1,34 @@
+LAMMPS data file via write_data, version 24 Dec 2020, timestep = 0
+
+4 atoms
+3 atom types
+
+0 1 xlo xhi
+0 1 ylo yhi
+-10 10 zlo zhi
+
+Masses
+
+1 196.966553
+2 196.966553
+3 1.0
+
+Pair Coeffs # lj/cut/coul/long
+
+1 0 0
+2 0 0
+3 0 0
+
+Atoms # full
+
+1 1 1  0.00 0.00 0.00 -2.00 # bottom electrode
+2 2 2  0.00 0.00 0.00  2.00 # top electrode
+3 3 3  0.50 0.00 0.00 -1.00 # bottom electrolyte
+4 3 3 -0.50 0.00 0.00  1.00 # top electrolyte
+
+ETA
+
+1 2.0
+2 2.0
+3 0
+4 0

examples/PACKAGES/electrode/madelung/data.eta_mix

@@ -0,0 +1,34 @@
+LAMMPS data file via write_data, version 24 Dec 2020, timestep = 0
+
+4 atoms
+3 atom types
+
+0 1 xlo xhi
+0 1 ylo yhi
+-10 10 zlo zhi
+
+Masses
+
+1 196.966553
+2 196.966553
+3 1.0
+
+Pair Coeffs # lj/cut/coul/long
+
+1 0 0
+2 0 0
+3 0 0
+
+Atoms # full
+
+1 1 1  0.00 0.00 0.00 -2.00 # bottom electrode
+2 2 2  0.00 0.00 0.00  2.00 # top electrode
+3 3 3  0.50 0.00 0.00 -1.00 # bottom electrolyte
+4 3 3 -0.50 0.00 0.00  1.00 # top electrolyte
+
+ETA
+
+1 0.5
+2 3.0
+3 0
+4 0

examples/PACKAGES/electrode/madelung/eval.py

@@ -1,7 +1,7 @@
 #!/usr/env/python3
 
-import sys
 import os.path as op
+import sys
 
 
 def rel_error(out, ref):
@@ -49,5 +49,5 @@ for label, ref, out in out_lines:
     error = rel_error(out, ref)
     lines.append(f"{label}: {out:.5f}, {error:.5f}\n")
 
-with open("madelung.txt", 'a') as f:
+with open("madelung.txt", "a") as f:
     f.writelines(lines)

examples/PACKAGES/electrode/madelung/in.eta

@@ -0,0 +1,17 @@
+atom_style full
+units real
+boundary p p f
+
+kspace_style ewald/electrode 1.0e-8
+kspace_modify slab 8.0 # ew3dc
+pair_style lj/cut/coul/long 12
+
+fix feta all property/atom d_eta ghost yes
+read_data data.eta fix feta NULL ETA
+
+include "settings_eta.mod"
+
+fix conp bot electrode/conp 0 2 couple top 1 symm on eta d_eta write_inv inv.csv write_vec vec.csv
+
+run 0
+

examples/PACKAGES/electrode/madelung/in.eta_cg

@@ -0,0 +1,17 @@
+atom_style full
+units real
+boundary p p f
+
+kspace_style ewald/electrode 1.0e-8
+kspace_modify slab 8.0 # ew3dc
+pair_style lj/cut/coul/long 12
+
+fix feta all property/atom d_eta ghost yes
+read_data data.eta_mix fix feta NULL ETA
+
+include "settings_eta.mod"
+
+fix conp bot electrode/conp 0 2 couple top 1 symm on algo cg 1e-6 eta d_eta
+
+run 0
+

examples/PACKAGES/electrode/madelung/in.eta_mix

@@ -0,0 +1,17 @@
+atom_style full
+units real
+boundary p p f
+
+kspace_style ewald/electrode 1.0e-8
+kspace_modify slab 8.0 # ew3dc
+pair_style lj/cut/coul/long 12
+
+fix feta all property/atom d_eta ghost on
+read_data data.eta_mix fix feta NULL ETA
+
+include "settings_eta.mod"
+
+fix conp bot electrode/conp 0 2 couple top 1 symm on eta d_eta write_inv inv.csv write_vec vec.csv
+
+run 0
+

examples/PACKAGES/electrode/madelung/plate_cap.py

@@ -3,7 +3,6 @@
 import numpy as np
 from scipy.special import erf
 
-ETA = 2
 SQRT2 = np.sqrt(2)
 COULOMB = 332.06371  #  Coulomb constant in Lammps 'real' units
 QE2F = 23.060549
@@ -17,14 +16,14 @@ def lattice(length):
     return np.array(np.meshgrid(x, y)).T.reshape(-1, 2)
 
 
-def a_element(r):
+def a_element(r, eta):
     """Coulomb contribution of two Gaussians"""
-    return erf(ETA / SQRT2 * r) / r
+    return erf(eta * r) / r
 
 
-def b_element(r, q):
+def b_element(r, q, eta):
     """Coulomb contribution of a Gaussian with a point charge"""
-    return q * erf(ETA * r) / r
+    return q * erf(eta * r) / r
 
 
 a = 1  # nearest neighbor distance i.e. lattice constant / sqrt(2)
@@ -36,49 +35,54 @@ v = np.array([-0.5, 0.5]) * (QE2F / COULOMB)
 
 # distances to images within electrode and to opposite electrode
 distances = a * np.linalg.norm(lattice(LENGTH), axis=1)
-opposite_distances = np.sqrt(np.square(distances) + distance_plates ** 2)
+opposite_distances = np.sqrt(np.square(distances) + distance_plates**2)
 
-# self interaction and within original box
+for name, eta_elec in [("", [2.0, 2.0]), ("_eta_mix", [0.5, 3.0])]:
-A_11 = np.sqrt(2 / np.pi) * ETA
+    eta_mix = np.prod(eta_elec) / np.sqrt(np.sum(np.square(eta_elec)))
-A_12 = erf(ETA * distance_plates / SQRT2) / distance_plates
+    # self interaction and within original box
+    A_11 = np.sqrt(2 / np.pi) * eta_elec[0]
+    A_22 = np.sqrt(2 / np.pi) * eta_elec[1]
+    A_12 = erf(eta_mix * distance_plates) / distance_plates
 
-# interaction with periodic images
+    # interaction with periodic images
-A_11 += 4 * np.sum(a_element(distances))
+    A_11 += 4 * np.sum(a_element(distances, eta_elec[0] / SQRT2))
-A_12 += 4 * np.sum(a_element(opposite_distances))
+    A_22 += 4 * np.sum(a_element(distances, eta_elec[1] / SQRT2))
-A = np.array([[A_11, A_12], [A_12, A_11]])
+    A_12 += 4 * np.sum(a_element(opposite_distances, eta_mix))
-inv = np.linalg.inv(A)
+    A = np.array([[A_11, A_12], [A_12, A_22]])
-e = np.array([1, 1])
+    inv = np.linalg.inv(A)
-inv -= np.matmul(inv, np.matmul(np.outer(e, e), inv)) / np.dot(e, np.dot(inv, e))
+    e = np.array([1, 1])
+    inv -= np.matmul(inv, np.matmul(np.outer(e, e), inv)) / np.dot(e, np.dot(inv, e))
 
-# electrode-electrolyte interaction
+    # electrode-electrolyte interaction
-b = []
+    b = []
-for x in x_elec:
+    for x, eta in zip(x_elec, eta_elec):
         bi = 0
         for y, q in zip(x_elyt, q_elyt):
             d = abs(y - x)
-        bi += b_element(d, q)
+            bi += b_element(d, q, eta)
-        image_distances = np.sqrt(np.square(distances) + d ** 2)
+            image_distances = np.sqrt(np.square(distances) + d**2)
-        bi += 4 * np.sum(b_element(image_distances, q))
+            bi += 4 * np.sum(b_element(image_distances, q, eta))
         b.append(bi)
-b = np.array(b)
+    b = np.array(b)
 
-# electrolyte-electrolyte energy
+    # electrolyte-electrolyte energy
-elyt_11 = 4 * np.sum(1 / distances)
+    elyt_11 = 4 * np.sum(1 / distances)
-distance_elyt = x_elyt[1] - x_elyt[0]
+    distance_elyt = x_elyt[1] - x_elyt[0]
-elyt_12 = 1 / distance_elyt + 4 * np.sum(
+    elyt_12 = 1 / distance_elyt + 4 * np.sum(
-    1 / np.sqrt(np.square(distances) + distance_elyt ** 2)
+        1 / np.sqrt(np.square(distances) + distance_elyt**2)
-)
+    )
-elyt = np.array([[elyt_11, elyt_12], [elyt_12, elyt_11]])
+    elyt = np.array([[elyt_11, elyt_12], [elyt_12, elyt_11]])
-energy_elyt = 0.5 * np.dot(q_elyt, np.dot(elyt, q_elyt))
+    energy_elyt = 0.5 * np.dot(q_elyt, np.dot(elyt, q_elyt))
 
-# electrode charges and energy
+    # electrode charges and energy
-q = np.dot(inv, v - b)
+    q = np.dot(inv, v - b)
-energy = COULOMB * (0.5 * np.dot(q, np.dot(A, q)) + np.dot(b, q) + energy_elyt)
+    energy = COULOMB * (0.5 * np.dot(q, np.dot(A, q)) + np.dot(b, q) + energy_elyt)
 
-print(
+    with open(f"plate_cap{name}.csv", "w") as f:
-    "length, energy / kcal/mol, q1 / e, q2 / e, inv11 / A, inv12 / A, b1 / e/A, b2 / e/A"
+        f.write(
-)
+            "length, energy / kcal/mol, q1 / e, q2 / e, inv11 / A, inv12 / A, b1 / e/A, b2 / e/A\n"
-print(
+        )
+        f.write(
             ", ".join(
                 [
                     str(LENGTH),
@@ -91,4 +95,5 @@ print(
                     f"{b[1]:.8f}",
                 ]
             )
-)
+            + "\n"
+        )

examples/PACKAGES/electrode/madelung/settings_eta.mod

@@ -0,0 +1,19 @@
+
+# distribute electrode atoms among all processors:
+if "$(extract_setting(world_size) % 2) == 0" then "processors * * 2"
+
+group bot type 1
+group top type 2
+
+# get electrode charges
+variable q atom q
+compute qbot bot reduce sum v_q
+compute qtop top reduce sum v_q
+
+compute compute_pe all pe
+variable vpe equal c_compute_pe
+variable charge equal c_qtop
+fix fxprint all print 1 "${vpe}, ${charge}" file "out.csv"
+
+thermo_style custom step pe c_qbot c_qtop
+

examples/PACKAGES/electrode/madelung/test.sh

@@ -7,17 +7,27 @@ if [ ! -f $lmpbin ]; then
 fi
 
 ref_out="plate_cap.csv"
-if [ ! -f $ref_out ]; then
+ref_mix_out="plate_cap_eta_mix.csv"
+if [ ! -f $ref_out ] || [ ! -f $ref_mix_out ]; then
     echo "Generating reference data"
-    python3 plate_cap.py > $ref_out
+    python3 plate_cap.py
 fi
 
 echo "Running Lammps inputs"
+# w/o eta mixing
 rm -rf madelung.txt && touch madelung.txt
-for file in in.*; do
+for file in in.eta in.ewald-ew3dc in.ewald-ew2d in.pppm-ew3dc in.cg; do
     printf "\n$file\n" >> madelung.txt
     rm -f out.csv inv.csv vec.csv 
     $lmpbin -i $file &> /dev/null
     python3 eval.py $ref_out out.csv inv.csv vec.csv
 done
+
+# with eta mixing
+for file in in.eta_mix in.eta_cg; do
+    printf "\n$file\n" >> madelung.txt
+    rm -f out.csv inv.csv vec.csv 
+    $lmpbin -i $file &> /dev/null
+    python3 eval.py $ref_mix_out out.csv inv.csv vec.csv
+done
 cat madelung.txt

src/ELECTRODE/electrode_matrix.cpp

@@ -43,6 +43,7 @@ ElectrodeMatrix::ElectrodeMatrix(LAMMPS *lmp, int electrode_group, double eta) :
   groupbit = group->bitmask[igroup];
   ngroup = group->count(igroup);
   this->eta = eta;
+  etaflag = false;
   tfflag = false;
 }
 
@@ -72,6 +73,14 @@ void ElectrodeMatrix::setup_tf(const std::map<int, double> &tf_types)
 
 /* ---------------------------------------------------------------------- */
 
+void ElectrodeMatrix::setup_eta(int index)
+{
+  etaflag = true;
+  eta_index = index;
+}
+
+/* ---------------------------------------------------------------------- */
+
 void ElectrodeMatrix::compute_array(double **array, bool timer_flag)
 {
   // setting all entries of coulomb matrix to zero
@@ -115,8 +124,6 @@ void ElectrodeMatrix::pair_contribution(double **array)
   int nlocal = atom->nlocal;
   int newton_pair = force->newton_pair;
 
-  double const etaij = eta * eta / sqrt(2.0 * eta * eta);    // see mw ewald theory eq. (29)-(30)
-
   // neighbor list will be ready because called from post_neighbor
   inum = list->inum;
   ilist = list->ilist;
@@ -135,6 +142,7 @@ void ElectrodeMatrix::pair_contribution(double **array)
     xtmp = x[i][0];
     ytmp = x[i][1];
     ztmp = x[i][2];
+    double const eta_i = etaflag ? atom->dvector[eta_index][i] : eta;
     itype = type[i];
     jlist = firstneigh[i];
     jnum = numneigh[i];
@@ -152,6 +160,9 @@ void ElectrodeMatrix::pair_contribution(double **array)
       jtype = type[j];
 
       if (rsq < cutsq[itype][jtype]) {
+        double const eta_j = etaflag ? atom->dvector[eta_index][j] : eta;
+        double const etaij = eta_i * eta_j / sqrt(eta_i * eta_i + eta_j * eta_j);
+
         r = sqrt(rsq);
         rinv = 1.0 / r;
         aij = rinv;
@@ -178,7 +189,10 @@ void ElectrodeMatrix::self_contribution(double **array)
   const double preta = MY_SQRT2 / MY_PIS;
 
   for (int i = 0; i < nlocal; i++)
-    if (mask[i] & groupbit) { array[mpos[i]][mpos[i]] += preta * eta - selfint; }
+    if (mask[i] & groupbit) {
+      double const eta_i = etaflag ? atom->dvector[eta_index][i] : eta;
+      array[mpos[i]][mpos[i]] += preta * eta_i - selfint;
+    }
 }
 
 /* ---------------------------------------------------------------------- */

src/ELECTRODE/electrode_matrix.h

@@ -30,6 +30,7 @@ class ElectrodeMatrix : protected Pointers {
   ElectrodeMatrix(class LAMMPS *, int, double);
   void setup(const std::unordered_map<tagint, int> &, class Pair *, class NeighList *);
   void setup_tf(const std::map<int, double> &);
+  void setup_eta(int);
   void compute_array(double **, bool);
   int igroup;
 
@@ -39,6 +40,8 @@ class ElectrodeMatrix : protected Pointers {
   double **cutsq;
   double g_ewald, eta;
   bool tfflag;
+  bool etaflag;
+  int eta_index;
   std::map<int, double> tf_types;
   std::unordered_map<tagint, int> tag_to_iele;
   bool assigned;

src/ELECTRODE/electrode_vector.cpp

@@ -29,6 +29,7 @@
 #include "neigh_list.h"
 #include "pair.h"
 
+#include <cassert>
 #include <cmath>
 #include <exception>
 
@@ -47,6 +48,7 @@ ElectrodeVector::ElectrodeVector(LAMMPS *lmp, int sensor_group, int source_group
   source_grpbit = group->bitmask[source_group];
   this->eta = eta;
   tfflag = false;
+  etaflag = false;
 
   kspace_time_total = 0;
   pair_time_total = 0;
@@ -93,6 +95,14 @@ void ElectrodeVector::setup_tf(const std::map<int, double> &tf_types)
 
 /* ---------------------------------------------------------------------- */
 
+void ElectrodeVector::setup_eta(int index)
+{
+  etaflag = true;
+  eta_index = index;
+}
+
+/* ---------------------------------------------------------------------- */
+
 void ElectrodeVector::compute_vector(double *vector)
 {
   MPI_Barrier(world);
@@ -121,7 +131,6 @@ void ElectrodeVector::compute_vector(double *vector)
 
 void ElectrodeVector::pair_contribution(double *vector)
 {
-  double const etaij = eta * MY_ISQRT2;
   double **x = atom->x;
   double *q = atom->q;
   int *type = atom->type;
@@ -142,6 +151,7 @@ void ElectrodeVector::pair_contribution(double *vector)
     double const xtmp = x[i][0];
     double const ytmp = x[i][1];
     double const ztmp = x[i][2];
+    double const eta_i = etaflag ? atom->dvector[eta_index][i] : eta;
     int itype = type[i];
     int *jlist = firstneigh[i];
     int jnum = numneigh[i];
@@ -158,18 +168,22 @@ void ElectrodeVector::pair_contribution(double *vector)
       double const rsq = delx * delx + dely * dely + delz * delz;
       int jtype = type[j];
       if (rsq >= cutsq[itype][jtype]) continue;
+      double const eta_j = etaflag ? atom->dvector[eta_index][j] : eta;
+      double etaij;
+      if (i_in_sensor && j_in_sensor)
+        etaij = eta_i * eta_j / sqrt(eta_i * eta_i + eta_j * eta_j);
+      else if (i_in_sensor)
+        etaij = eta_i;
+      else {
+        assert(j_in_sensor);
+        etaij = eta_j;
+      }
       double const r = sqrt(rsq);
       double const rinv = 1.0 / r;
       double aij = rinv;
       aij *= ElectrodeMath::safe_erfc(g_ewald * r);
-      if (invert_source)
-        aij -= ElectrodeMath::safe_erfc(eta * r) * rinv;
-      else
       aij -= ElectrodeMath::safe_erfc(etaij * r) * rinv;
-      if (i_in_sensor) {
+      if (i_in_sensor) { vector[i] += aij * q[j]; }
-        vector[i] += aij * q[j];
-        //} else if (j_in_sensor) {
-      }
       if (j_in_sensor && (!invert_source || !i_in_sensor)) { vector[j] += aij * q[i]; }
     }
   }
@@ -189,9 +203,10 @@ void ElectrodeVector::self_contribution(double *vector)
 
   for (int ii = 0; ii < inum; ii++) {
     int const i = ilist[ii];
+    double const eta_i = etaflag ? atom->dvector[eta_index][i] : eta;
     bool const i_in_sensor = (mask[i] & groupbit);
     bool const i_in_source = !!(mask[i] & source_grpbit) != invert_source;
-    if (i_in_sensor && i_in_source) vector[i] += (preta * eta - selfint) * q[i];
+    if (i_in_sensor && i_in_source) vector[i] += (preta * eta_i - selfint) * q[i];
   }
 }
 

src/ELECTRODE/electrode_vector.h

@@ -29,6 +29,7 @@ class ElectrodeVector : protected Pointers {
   ~ElectrodeVector() override;
   void setup(class Pair *, class NeighList *, bool);
   void setup_tf(const std::map<int, double> &);
+  void setup_eta(int);
   void compute_vector(double *);
   int igroup, source_group;
 
@@ -39,6 +40,8 @@ class ElectrodeVector : protected Pointers {
   double **cutsq;
   double g_ewald, eta;
   bool tfflag;
+  bool etaflag;
+  int eta_index;
   std::map<int, double> tf_types;
   class Pair *pair;
   class NeighList *list;

src/ELECTRODE/fix_electrode_conp.cpp

@@ -97,6 +97,7 @@ FixElectrodeConp::FixElectrodeConp(LAMMPS *lmp, int narg, char **arg) :
   top_group = 0;
   intelflag = false;
   tfflag = false;
+  etaflag = false;
   timer_flag = false;
 
   update_time = 0;
@@ -211,6 +212,19 @@ FixElectrodeConp::FixElectrodeConp(LAMMPS *lmp, int narg, char **arg) :
         qtotal = utils::numeric(FLERR, arg[iarg], false, lmp);
         qtotal_var_style = VarStyle::CONST;
       }
+    } else if ((strcmp(arg[iarg], "eta") == 0)) {
+      if (iarg + 2 > narg) error->all(FLERR, "Need two arguments after eta command");
+      etaflag = true;
+      int is_double, cols;
+      eta_index = atom->find_custom(arg[++iarg] + 2, is_double, cols);
+      if (eta_index == -1)
+        error->all(FLERR, "eta keyword requires name of previously defined property");
+      if (!is_double) error->all(FLERR, "eta keyword requires double-valued property/atom vector");
+      if (cols != 0) error->all(FLERR, "eta keyword requires property/atom vector not an array");
+      if (!atom->nextra_border)
+        error->all(FLERR,
+                   "There is no fix with ghost on, but the eta keyword requires a property/atom "
+                   "fix with ghost on");
       // toggle parameters
     } else if ((strcmp(arg[iarg], "etypes") == 0)) {
       etypes_neighlists = utils::logical(FLERR, arg[++iarg], false, lmp);
@@ -520,8 +534,10 @@ void FixElectrodeConp::setup_post_neighbor()
 
   evscale = force->qe2f / force->qqrd2e;
   elyt_vector->setup(pair, vec_neighlist, timer_flag);
+  if (etaflag) elyt_vector->setup_eta(eta_index);
   if (need_elec_vector) {
     elec_vector->setup(pair, mat_neighlist, timer_flag);
+    if (etaflag) elec_vector->setup_eta(eta_index);
     if (tfflag) elec_vector->setup_tf(tf_types);
   }
 
@@ -556,7 +572,8 @@ void FixElectrodeConp::setup_post_neighbor()
       if (etypes_neighlists) neighbor->build_one(mat_neighlist, 0);
       auto array_compute = std::unique_ptr<ElectrodeMatrix>(new ElectrodeMatrix(lmp, igroup, eta));
       array_compute->setup(tag_to_iele, pair, mat_neighlist);
-      if (tfflag) { array_compute->setup_tf(tf_types); }
+      if (etaflag) array_compute->setup_eta(eta_index);
+      if (tfflag) array_compute->setup_tf(tf_types);
       array_compute->compute_array(elastance, timer_flag);
     }    // write_mat before proceeding
     if (comm->me == 0 && write_mat) {
@@ -1186,7 +1203,7 @@ double FixElectrodeConp::self_energy(int eflag)
   // corrections to energy due to self interaction
   double const qqrd2e = force->qqrd2e;
   int const nlocal = atom->nlocal;
-  double const pre = eta / sqrt(MY_2PI) * qqrd2e;
+  double const pre = 1. / sqrt(MY_2PI) * qqrd2e;
   int *mask = atom->mask;
   int *type = atom->type;
   double *q = atom->q;
@@ -1194,7 +1211,8 @@ double FixElectrodeConp::self_energy(int eflag)
   for (int i = 0; i < nlocal; i++) {
     if (groupbit & mask[i]) {
       double const q2 = q[i] * q[i];
-      double e = pre * q2;
+      double ieta = etaflag ? atom->dvector[eta_index][i] : eta;
+      double e = ieta * pre * q2;
       if (tfflag && (groupbit & mask[i])) e += 0.5 * qqrd2e * q2 * tf_types[type[i]];
       energy += e;
       if (eflag) {
@@ -1234,6 +1252,7 @@ double FixElectrodeConp::gausscorr(int eflag, bool fflag)
     double xtmp = x[i][0];
     double ytmp = x[i][1];
     double ztmp = x[i][2];
+    double const eta_i = etaflag ? atom->dvector[eta_index][i] : eta;
     int itype = type[i];
     int *jlist = firstneigh[i];
     int jnum = numneigh[i];
@@ -1242,7 +1261,6 @@ double FixElectrodeConp::gausscorr(int eflag, bool fflag)
       int const j = jlist[jj] & NEIGHMASK;
       bool j_in_ele = groupbit & mask[j];
       if (!(i_in_ele || j_in_ele)) continue;
-      double eta_ij = (i_in_ele && j_in_ele) ? eta / MY_SQRT2 : eta;
 
       double delx = xtmp - x[j][0];
       double dely = ytmp - x[j][1];
@@ -1251,6 +1269,16 @@ double FixElectrodeConp::gausscorr(int eflag, bool fflag)
       int jtype = type[j];
 
       if (rsq < force->pair->cutsq[itype][jtype]) {
+        double const eta_j = etaflag ? atom->dvector[eta_index][j] : eta;
+        double eta_ij;
+        if (i_in_ele && j_in_ele)
+          eta_ij = eta_i * eta_j / sqrt(eta_i * eta_i + eta_j * eta_j);
+        else if (i_in_ele)
+          eta_ij = eta_i;
+        else {
+          assert(j_in_ele);
+          eta_ij = eta_j;
+        }
         double r2inv = 1.0 / rsq;
         double r = sqrt(rsq);
         double erfc_etar = 0.;

src/ELECTRODE/fix_electrode_conp.h

@@ -138,6 +138,8 @@ class FixElectrodeConp : public Fix {
   int get_top_group();    // used by ffield
   int top_group;          // used by ffield
   bool tfflag;
+  int eta_index;    // index of atom property for eta
+  bool etaflag;     // eta specified as atom property
   bool timer_flag;
   std::map<int, double> tf_types;
   // cg