External potentials add to the acceleration. They don't overwrite it.

src/cooling/const_lambda/cooling.h

@@ -48,7 +48,7 @@ __attribute__((always_inline)) INLINE static float cooling_rate(
     const struct cooling_function_data* cooling, const struct part* p) {
 
   /* Get particle density */
-  const float rho = p->rho;
+  const float rho = hydro_get_density(p);
 
   /* Get cooling function properties */
   const float X_H = cooling->hydrogen_mass_abundance;
@@ -91,6 +91,7 @@ __attribute__((always_inline)) INLINE static void cooling_cool_part(
   } else {
     u_new = u_floor;
   }
+
   /* Update the internal energy */
   hydro_set_internal_energy(p, u_new);
 

src/cooling/const_lambda/cooling_struct.h

@@ -28,7 +28,7 @@
  */
 struct cooling_function_data {
 
-  /*! Cooling rate in cgs units. Defined by 'rho * du/dt = -lambda * n_H^2'*/
+  /*! Cooling rate in internal units */
   double lambda;
 
   /*! Fraction of gas mass that is Hydrogen. Used to calculate n_H */

src/potential/isothermal/potential.h

@@ -107,13 +107,13 @@ __attribute__((always_inline)) INLINE static void external_gravity_acceleration(
   const float dy = g->x[1] - potential->y;
   const float dz = g->x[2] - potential->z;
 
-  const float rinv2 = 1. / (dx * dx + dy * dy + dz * dz);
+  const float rinv2 = 1.f / (dx * dx + dy * dy + dz * dz);
 
   const double term = -potential->vrot2_over_G * rinv2;
 
-  g->a_grav[0] = term * dx;
-  g->a_grav[1] = term * dy;
-  g->a_grav[2] = term * dz;
+  g->a_grav[0] += term * dx;
+  g->a_grav[1] += term * dy;
+  g->a_grav[2] += term * dz;
 }
 
 /**

src/potential/softened_isothermal/potential.h

@@ -118,9 +118,9 @@ __attribute__((always_inline)) INLINE static void external_gravity_acceleration(
 
   const double term = -potential->vrot2_over_G * r2_plus_epsilon2_inv;
 
-  g->a_grav[0] = term * dx;
-  g->a_grav[1] = term * dy;
-  g->a_grav[2] = term * dz;
+  g->a_grav[0] += term * dx;
+  g->a_grav[1] += term * dy;
+  g->a_grav[2] += term * dz;
 }
 
 /**

src/runner.c

@@ -52,7 +52,6 @@
 #include "hydro_properties.h"
 #include "kick.h"
 #include "minmax.h"
-#include "potential.h"
 #include "scheduler.h"
 #include "sourceterms.h"
 #include "space.h"