code: def bm3_g(p, v0, g0, g0p, k0, k0p):
      
      return cal_g_bm3(p, [g0, g0p], [v0, k0, k0p])
docs: calculate shear modulus at given pressure.
      not fully tested with mdaap.
  
      :param p: pressure
      :param v0: volume at reference condition
      :param g0: shear modulus at reference condition
      :param g0p: pressure derivative of shear modulus at reference condition
      :param k0: bulk modulus at reference condition
      :param k0p: pressure derivative of bulk modulus at reference condition
      :return: shear modulus at high pressure