text: from math import pi
  import simtk.unit as u
  
  kB = u.BOLTZMANN_CONSTANT_kB * u.AVOGADRO_CONSTANT_NA
  
  # OpenMM constant for Coulomb interactions in OpenMM units
  # (openmm/platforms/reference/include/SimTKOpenMMRealType.h)
  # TODO: Replace this with an import from simtk.openmm.constants once available
  E_CHARGE = 1.602176634e-19 * u.coulomb
  EPSILON0 = 1e-6*8.8541878128e-12/(u.AVOGADRO_CONSTANT_NA*E_CHARGE**2) * u.farad/u.meter
  ONE_4PI_EPS0 = 1/(4*pi*EPSILON0) * EPSILON0.unit  # we need it unitless
  
  # Standard-state volume for a single molecule in a box of size (1 L) / (avogadros number).
  LITER = 1000.0 * u.centimeters**3
  STANDARD_STATE_VOLUME = LITER / (u.AVOGADRO_CONSTANT_NA*u.mole)
  