Image Method


Surface charging or polarization can strongly affect the nature of interactions between charged dielectric objects, particularly when sharp dielectric discontinuities are involved. However, not any efficient and accurate computation tools are publicly available especially for the description of polarization effects in many-body systems.

For this purpose, Image Method, an analytic perturbative approach we recently developed for evaluating the polarization energy of a many-body collection of charged dielectric spheres embedded in a dielectric medium becomes particularly suitable [1].

The polarization-induced interactions between these spheres depend on the ratio of dielectric constants for the spheres and the medium, and the ratio of the distance between particles and the radii of the particles. We have shown that, in some cases, polarization completely alters the qualitative behavior, and in some other cases, polarization leads to stable configurations that otherwise could not occur in its absence.

We think it is helpful to include Image Method into SSAGES for users to include polarization corrections properly in their systems, and meanwhile, to couple with advanced sampling methods to accelerate their simulations.

Options & Parameters

SSAGES Image method is implemented in a way that is as easy as conducting a simulation using LAMMPS that only includes pairwise Coulombic interactions into electrostatic interactions. To achieve this, we update the electrostatic forces acting on all objects by adding up the polarization corrections using SSAGES engine and then pass the modified snapshot back to LAMMPS engine at each time step. The JSON file needed for SSAGES engine should include:

The relative dielectric permittivity of polarizable object.
For cases that you have both polarizable objects and non-polarizable objects in you system, for example, in which colloids and ions are treated as polarizable and non-polarizable, respectively. This parameter controls where the non-polarizable typos start.
atom type radius
Radius of all types of objects.


It is very similar as running a simulation including electrostatic interactions using LAMMPS. Referring to the exampled LAMMPS INPUTFILE and DATAFILE, you need to double check you have declared the following variables that are particularly necessary for Image Method to compute polarization corrections:

  • charges
  • dielectric (relative dielectric permittivity of the surrounding continuum)

Method Output

There are not special outputs files generated for Image method since it only provides an updated electrostatic forces by including polarization corrections. Nevertheless, we provided options of dumping trajectories and printing out force-distance data in the LAMMPS INPUTFILE examples for users to visualize how significant the polarization effects are in some cases more conveniently.



Write a tutorial.


Jiyuan Li.


[1]J. Qin, J. Li, V. Lee, H. Jaeger, J. J. de Pablo, and K. Freed, A theory of interactions between polarizable dielectric spheres, J. Coll. Int. Sci. 469, 237 - 241 (2016)