Add Gay-Berne interaction with tunable radial width

src/config/features.def

@@ -78,6 +78,7 @@ BUCKINGHAM
 SOFT_SPHERE
 HAT
 GAY_BERNE                       implies ROTATION
+GAY_BERNE_WIDTH                 implies ROTATION
 THOLE                           requires ELECTROSTATICS
 
 /* ScaFaCoS */

src/core/energy_inline.hpp

@@ -34,6 +34,7 @@
 #include "nonbonded_interactions/buckingham.hpp"
 #include "nonbonded_interactions/gaussian.hpp"
 #include "nonbonded_interactions/gay_berne.hpp"
+#include "nonbonded_interactions/gay_berne_width.hpp"
 #include "nonbonded_interactions/hat.hpp"
 #include "nonbonded_interactions/hertzian.hpp"
 #include "nonbonded_interactions/lj.hpp"
@@ -175,6 +176,10 @@ inline double calc_non_bonded_pair_energy(
   ret += gb_pair_energy(p1.quat(), p2.quat(), ia_params, d, dist);
 #endif
 
+#ifdef ESPRESSO_GAY_BERNE_WIDTH
+  ret += gb_width_pair_energy(p1.quat(), p2.quat(), ia_params, d, dist);
+#endif
+
   return ret;
 }
 

src/core/forces_inline.hpp

@@ -40,6 +40,7 @@
 #include "nonbonded_interactions/buckingham.hpp"
 #include "nonbonded_interactions/gaussian.hpp"
 #include "nonbonded_interactions/gay_berne.hpp"
+#include "nonbonded_interactions/gay_berne_width.hpp"
 #include "nonbonded_interactions/hat.hpp"
 #include "nonbonded_interactions/hertzian.hpp"
 #include "nonbonded_interactions/lj.hpp"
@@ -152,6 +153,11 @@ inline ParticleForce calc_non_central_force(Particle const &p1,
 #ifdef ESPRESSO_GAY_BERNE
   pf += gb_pair_force(p1.quat(), p2.quat(), ia_params, d, dist);
 #endif
+
+#ifdef ESPRESSO_GAY_BERNE_WIDTH
+  pf += gb_width_pair_force(p1.quat(), p2.quat(), ia_params, d, dist);
+#endif
+
   return pf;
 }
 
@@ -166,6 +172,11 @@ inline Utils::Vector3d calc_non_central_force(Utils::Vector3d const &dir1,
 #ifdef ESPRESSO_GAY_BERNE
   f += gb_pair_force(dir1, dir2, ia_params, d, dist).f;
 #endif
+
+#ifdef ESPRESSO_GAY_BERNE_WIDTH
+  f += gb_width_pair_force(dir1, dir2, ia_params, d, dist).f;
+#endif
+
   return f;
 }
 

src/core/nonbonded_interactions/CMakeLists.txt

@@ -23,6 +23,7 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/buckingham.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/gaussian.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/gay_berne.cpp
+          ${CMAKE_CURRENT_SOURCE_DIR}/gay_berne_width.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/hat.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/hertzian.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/ljcos2.cpp

src/core/nonbonded_interactions/gay_berne_width.cpp

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2010-2026 The ESPResSo project
+ *
+ * This file is part of ESPResSo.
+ *
+ * ESPResSo is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ESPResSo is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** \file
+ *
+ * Implementation of \ref gay_berne_width.hpp
+ */
+
+#include "gay_berne_width.hpp"
+
+#ifdef ESPRESSO_GAY_BERNE_WIDTH
+
+#include "nonbonded_interaction_data.hpp"
+
+#include <cmath>
+
+GayBerneWidth_Parameters::GayBerneWidth_Parameters(double eps, double sig,
+                                                   double wid, double cut,
+                                                   double k1, double k2,
+                                                   double mu, double nu)
+    : eps{eps}, sig{sig}, wid{wid}, cut{cut}, k1{k1}, k2{k2}, mu{mu}, nu{nu},
+      chi1{((k1 * k1) - 1.) / ((k1 * k1) + 1.)},
+      chi2{(std::pow(k2, 1. / mu) - 1.) / (std::pow(k2, 1. / mu) + 1.)} {}
+
+#endif // ESPRESSO_GAY_BERNE_WIDTH