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+====== Stephens_peakshape ======
+Description: Stephens peak shape broadening macros
+Contributed by: Peter Stephens, Robert Dinnebier, Andreas Leinweber
+An alternative approach to spherical harmonics for hkl dependent peak shapes by
+Peter Stephens (P.W. Stephens, J. Appl. Cryst. (1999) 32, 281-9) as coded in gsas.
+eta term allows mixture of Gauss/Lorentz broadening.
+Built in macros for different point groups are:
+<code topas>
+Stephens_triclinic (-1)
+Stephens_monoclinic (2/m)
+Stephens_orthorhombic (mmm)
+Stephens_tetragonal_low (4/m)
+Stephens_tetragonal_high (4/mmm)
+Stephens_trigonal_low (-3)
+Stephens_trigonal_high (-3m1)
+Stephens_trigonal_high_2 (-31m)
+Stephens_hexagonal (6/m and 6/mmm)
+Stephens_cubic (m-3 and m-3m)
+</code>
+Note that for all trigonal Laue classes the macros assume the hexagonal setting of the unit cell
+As an example try the following in your input file (macros you need are below).  Look in topas.inc to double-check the format of macros:
+<code topas>prm s400 11769.84126`
+prm s004 153.55044`
+prm s220 28029.32854`
+prm s202 -1067.03124`
+prm eta 0.52180` min 0 max 1
+</code>
+Stephens_tetragonal(s400, s004, s220, s202, eta)
+<code topas>
+macro Stephens_tetragonal(s400, s004, s220, s202, eta)
+{
+prm mhkl = Abs(s400 (H^4+ K^4)+ s004 L^4+ s220 H^2 K^2 + s202 (H^2 L^2 + K^2 L^2) );
+prm pp = D_spacing^2 * Sqrt(Max(mhkl,0)) / 1000;
+gauss_fwhm = 1.8/3.1415927 pp (1-eta) Tan(Th) + 0.0001;
+lor_fwhm = 1.8/3.1415927 pp eta Tan(Th) + 0.0001;
+}
+</code>
+Stephens_monoclinic(s400, s040, s004, s220, s202, s022, s301, s121, s103, eta)
+<code topas>
+macro Stephens_monoclinic(s400, s040, s004, s220, s202, s022, s301, s121, s103, eta)
+{
+prm mhkl = H^4 s400 + K^4 s040 + L^4 s004 +
+H^2 K^2 s220 + H^2 L^2 s202 + K^2 L^2 s022 +
+H K^2 L s121 +
+H L^3 s103 + H^3 L s301;
+prm pp = D_spacing^2 * Sqrt(Max(mhkl,0)) / 1000;
+gauss_fwhm = 1.8/3.1415927 pp (1-eta) Tan(Th) + 0.0001;
+lor_fwhm = 1.8/3.1415927 pp eta Tan(Th) + 0.0001;
+}
+</code>
+Stephens_hexagonal(s400, s202, s004, eta)
+<code topas>
+macro Stephens_hexagonal(s400, s202, s004, eta)
+{
+prm mhkl = H^4 s400 + K^4 s400 + L^4 s004 +
+H^2 K^2 3 s400 + H^2 L^2 s202 + K^2 L^2 s202 +
+H K L^2 s202 +
+H^3 K 2 s400 + H K^3 2 s400;
+prm pp = D_spacing^2 * Sqrt(Max(mhkl,0)) / 1000;
+gauss_fwhm = 1.8/3.1415927 pp (1-eta) Tan(Th) + 0.0001;
+lor_fwhm = 1.8/3.1415927 pp eta Tan(Th) + 0.0001;
+}
+</code>
+Stephens_orthorhombic(s400, s040, s004, s220, s202, s022, eta)
+<code topas>
+macro Stephens_orthorhombic(s400, s040, s004, s220, s202, s022, eta)
+{
+prm mhkl = H^4 s400 + K^4 s040 + L^4 s004 +
+H^2 K^2 s220 + H^2 L^2 s202 + K^2 L^2 s022;
+prm pp = D_spacing^2 * Sqrt(Max(mhkl,0)) / 1000;
+gauss_fwhm = 1.8/3.1415927 pp (1-eta) Tan(Th) + 0.0001;
+lor_fwhm = 1.8/3.1415927 pp eta Tan(Th) + 0.0001;
+}
+</code>