  We introduce TERMS, an open-source Fortran program to simulate near-field and
far-field optical properties of clusters of particles. The program solves
rigorously the Maxwell equations via the superposition T-matrix method, where
incident and scattered fields are decomposed into series of vector spherical
waves.
  TERMS implements several algorithms to solve the coupled system of multiple
scattering equations that describes the electromagnetic interaction between
neighbouring scatterers. From this formal solution, the program can compute a
number of physically-relevant optical properties, such as far-field
cross-sections for extinction, absorption, scattering and their corresponding
circular dichroism, as well as local field intensities and degree of optical
chirality. By describing the incident and scattered fields in a basis of
spherical waves the T-matrix framework lends itself to analytical formulas for
orientation-averaged quantities, corresponding to systems of particles in
random orientation; TERMS offers such computations for both far-field and
near-field quantities of interest. This user guide introduces the program,
summarises the relevant theory, and is supplemented by a comprehensive suite of
stand-alone examples in the website accompanying the code.
