13. GSASIIpwd: Powder calculations module

GSASIIpwd.Absorb(Geometry, MuR, Tth, Phi=0, Psi=0)

Calculate sample absorption :param str Geometry: one of ‘Cylinder’,’Bragg-Brentano’,’Tilting Flat Plate in transmission’,’Fixed flat plate’ :param float MuR: absorption coeff * sample thickness/2 or radius :param Tth: 2-theta scattering angle - can be numpy array :param float Phi: flat plate tilt angle - future :param float Psi: flat plate tilt axis - future

GSASIIpwd.AbsorbDerv(Geometry, MuR, Tth, Phi=0, Psi=0)

needs a doc string

GSASIIpwd.CalcPDF(data, inst, limits, xydata)

Computes I(Q), S(Q) & G(r) from Sample, Bkg, etc. diffraction patterns loaded into dict xydata; results are placed in xydata. Calculation parameters are found in dicts data and inst and list limits. The return value is at present an empty list.

GSASIIpwd.Dict2Values(parmdict, varylist)

Use before call to leastsq to setup list of values for the parameters in parmdict, as selected by key in varylist

GSASIIpwd.DoPeakFit(FitPgm, Peaks, Background, Limits, Inst, Inst2, data, fixback=None, prevVaryList=[], oneCycle=False, controls=None, wtFactor=1.0, dlg=None)

Called to perform a peak fit, refining the selected items in the peak table as well as selected items in the background.

Parameters:

• FitPgm (str) – type of fit to perform. At present this is ignored.
• Peaks (list) – a list of peaks. Each peak entry is a list with 8 values: four values followed by a refine flag where the values are: position, intensity, sigma (Gaussian width) and gamma (Lorentzian width). From the Histogram/”Peak List” tree entry, dict item “peaks”
• Background (list) – describes the background. List with two items. Item 0 specifies a background model and coefficients. Item 1 is a dict. From the Histogram/Background tree entry.
• Limits (list) – min and max x-value to use
• Inst (dict) – Instrument parameters
• Inst2 (dict) – more Instrument parameters
• data (numpy.array) – a 5xn array. data[0] is the x-values, data[1] is the y-values, data[2] are weight values, data[3], [4] and [5] are calc, background and difference intensities, respectively.
• fixback (array) – fixed background array; same size as data[0-5]
• prevVaryList (list) – Used in sequential refinements to override the variable list. Defaults as an empty list.
• oneCycle (bool) – True if only one cycle of fitting should be performed
• controls (dict) – a dict specifying two values, Ftol = controls[‘min dM/M’] and derivType = controls[‘deriv type’]. If None default values are used.
• wtFactor (float) – weight multiplier; = 1.0 by default
• dlg (wx.Dialog) – A dialog box that is updated with progress from the fit. Defaults to None, which means no updates are done.

GSASIIpwd.GetAsfMean(ElList, Sthl2)

Calculate various scattering factor terms for PDF calcs

Parameters:

• ElList (dict) – element dictionary contains scattering factor coefficients, etc.
• Sthl2 (np.array) – numpy array of sin theta/lambda squared values

Returns:

mean(f^2), mean(f)^2, mean(compton)

GSASIIpwd.GetNumDensity(ElList, Vol)

needs a doc string

GSASIIpwd.LorchWeight(Q)

needs a doc string

GSASIIpwd.MEMupdateReflData(prfName, data, reflData)

Update reflection data with new Fosq, phase result from Dysnomia

Parameters:

• prfName (str) – phase.mem file name
• reflData (list) – GSAS-II reflection data

GSASIIpwd.MakefullrmcRun(pName, Phase, RMCPdict)

Creates a script to run fullrmc. Returns the name of the file that was created.

GSASIIpwd.Oblique(ObCoeff, Tth)

currently assumes detector is normal to beam

GSASIIpwd.PhaseWtSum(G2frame, histo)

Calculate sum of phase mass*phase fraction for PWDR data (exclude magnetic phases)

Parameters:

• G2frame – GSASII main frame structure
• histo (str) – histogram name

Returns:

sum(scale*mass) for phases in histo

GSASIIpwd.Polarization(Pola, Tth, Azm=0.0)

Calculate angle dependent x-ray polarization correction (not scaled correctly!)

Parameters:

• Pola – polarization coefficient e.g 1.0 fully polarized, 0.5 unpolarized
• Azm – azimuthal angle e.g. 0.0 in plane of polarization - can be numpy array
• Tth – 2-theta scattering angle - can be numpy array which (if either) of these is “right”?

Returns:

(pola, dpdPola) - both 2-d arrays * pola = ((1-Pola)*npcosd(Azm)**2+Pola*npsind(Azm)**2)*npcosd(Tth)**2+ (1-Pola)*npsind(Azm)**2+Pola*npcosd(Azm)**2 * dpdPola: derivative needed for least squares

GSASIIpwd.Ruland(RulCoff, wave, Q, Compton)

needs a doc string

GSASIIpwd.SetBackgroundParms(Background)

Loads background parameters into dicts/lists to create varylist & parmdict

GSASIIpwd.StackSim(Layers, ctrls, scale=0.0, background={}, limits=[], inst={}, profile=[])

Simulate powder or selected area diffraction pattern from stacking faults using DIFFaX

Parameters:

• Layers (dict) –

  dict with following items

  {'Laue':'-1','Cell':[False,1.,1.,1.,90.,90.,90,1.],
  'Width':[[10.,10.],[False,False]],'Toler':0.01,'AtInfo':{},
  'Layers':[],'Stacking':[],'Transitions':[]}
  

• ctrls (str) – controls string to be written on DIFFaX controls.dif file
• scale (float) – scale factor
• background (dict) – background parameters
• limits (list) – min/max 2-theta to be calculated
• inst (dict) – instrument parameters dictionary
• profile (list) – powder pattern data

Note that parameters all updated in place

GSASIIpwd.SurfaceRough(SRA, SRB, Tth)

Suortti (J. Appl. Cryst, 5,325-331, 1972) surface roughness correction :param float SRA: Suortti surface roughness parameter :param float SRB: Suortti surface roughness parameter :param float Tth: 2-theta(deg) - can be numpy array

GSASIIpwd.SurfaceRoughDerv(SRA, SRB, Tth)

Suortti surface roughness correction derivatives :param float SRA: Suortti surface roughness parameter (dimensionless) :param float SRB: Suortti surface roughness parameter (dimensionless) :param float Tth: 2-theta(deg) - can be numpy array :return list: [dydSRA,dydSRB] derivatives to be used for intensity derivative

GSASIIpwd.TestData()

needs a doc string

GSASIIpwd.Transmission(Geometry, Abs, Diam)

Calculate sample transmission

Parameters:

• Geometry (str) – one of ‘Cylinder’,’Bragg-Brentano’,’Tilting flat plate in transmission’,’Fixed flat plate’
• Abs (float) – absorption coeff in cm-1
• Diam (float) – sample thickness/diameter in mm

GSASIIpwd.Values2Dict(parmdict, varylist, values)

Use after call to leastsq to update the parameter dictionary with values corresponding to keys in varylist

GSASIIpwd.abeles(kz, depth, rho, irho=0, sigma=0)

Optical matrix form of the reflectivity calculation. O.S. Heavens, Optical Properties of Thin Solid Films

Reflectometry as a function of kz for a set of slabs.

Parameters:

• kz – float[n] (1/Ang). Scattering vector, \(2\pi\sin(\theta)/\lambda\). This is \(\tfrac12 Q_z\).
• depth – float[m] (Ang). thickness of each layer. The thickness of the incident medium and substrate are ignored.
• rho – float[n,k] (1e-6/Ang^2) Real scattering length density for each layer for each kz
• irho – float[n,k] (1e-6/Ang^2) Imaginary scattering length density for each layer for each kz Note: absorption cross section mu = 2 irho/lambda for neutrons
• sigma – float[m-1] (Ang) interfacial roughness. This is the roughness between a layer and the previous layer. The sigma array should have m-1 entries.

Slabs are ordered with the surface SLD at index 0 and substrate at index -1, or reversed if kz < 0.

GSASIIpwd.calcIncident(Iparm, xdata)

needs a doc string

class GSASIIpwd.cauchy_gen(*args, **kwargs)

needs a doc string

GSASIIpwd.ellipseSize(H, Sij, GB)

Implements r=1/sqrt(sum((1/S)*(q.v)^2) per note from Alexander Brady

GSASIIpwd.ellipseSizeDerv(H, Sij, GB)

Implements r=1/sqrt(sum((1/S)*(q.v)^2) derivative per note from Alexander Brady

GSASIIpwd.factorize(num)

Provide prime number factors for integer num :returns: dictionary of prime factors (keys) & power for each (data)

class GSASIIpwd.fcjde_gen(*args, **kwargs)

Finger-Cox-Jephcoat D(2phi,2th) function for S/L = H/L Ref: J. Appl. Cryst. (1994) 27, 892-900.

Parameters:

• x – array -1 to 1
• t – 2-theta position of peak
• s – sum(S/L,H/L); S: sample height, H: detector opening, L: sample to detector opening distance
• dx – 2-theta step size in deg

Returns:

for fcj.pdf

• T = x*dx+t

• s = S/L+H/L

• if x < 0:

  fcj.pdf = [1/sqrt({cos(T)**2/cos(t)**2}-1) - 1/s]/|cos(T)| 
  

• if x >= 0: fcj.pdf = 0

GSASIIpwd.findfullrmc()

Find where fullrmc is installed. Tries the following:

1. Returns the Config var ‘fullrmc_exec’, if defined. No check is done that the interpreter has fullrmc
2. The current Python interpreter if fullrmc can be imported and fullrmc is version 5+
3. The path is checked for a fullrmc image as named by Bachir

Returns:the full path to a python executable that is assumed to have fullrmc installed or None, if it was not found.

GSASIIpwd.getBackground(pfx, parmDict, bakType, dataType, xdata, fixback=None)

Computes the background from vars pulled from gpx file or tree.

GSASIIpwd.getBackgroundDerv(hfx, parmDict, bakType, dataType, xdata, fixback=None)

needs a doc string

GSASIIpwd.getEpsVoigt(pos, alp, bet, sig, gam, xdata)

Compute the double exponential Pseudo-Voigt convolution function for a neutron TOF & CW pink peak in external Fortran routine

GSASIIpwd.getFCJVoigt(pos, intens, sig, gam, shl, xdata)

Compute the Finger-Cox-Jepcoat modified Voigt function for a CW powder peak by direct convolution. This version is not used.

GSASIIpwd.getFCJVoigt3(pos, sig, gam, shl, xdata)

Compute the Finger-Cox-Jepcoat modified Pseudo-Voigt function for a CW powder peak in external Fortran routine

param pos: peak position in degrees param sig: Gaussian variance in centideg^2 param gam: Lorentzian width in centideg param shl: axial divergence parameter (S+H)/L param xdata: array; profile points for peak to be calculated; bounded by 20FWHM to 50FWHM (or vv)

returns: array: calculated peak function at each xdata returns: integral of peak; nominally = 1.0

GSASIIpwd.getFWHM(pos, Inst)

Compute total FWHM from Thompson, Cox & Hastings (1987) , J. Appl. Cryst. 20, 79-83 via getgamFW(g,s).

Parameters:

• pos – float peak position in deg 2-theta or tof in musec
• Inst – dict instrument parameters

Returns float:

total FWHM of pseudoVoigt in deg or musec

GSASIIpwd.getHKLMpeak(dmin, Inst, SGData, SSGData, Vec, maxH, A)

needs a doc string

GSASIIpwd.getHKLpeak(dmin, SGData, A, Inst=None, nodup=False)

Generates allowed by symmetry reflections with d >= dmin NB: GenHKLf & checkMagextc return True for extinct reflections

Parameters:

• dmin – minimum d-spacing
• SGData – space group data obtained from SpcGroup
• A – lattice parameter terms A1-A6
• Inst – instrument parameter info

Returns:

HKLs: np.array hkl, etc for allowed reflections

GSASIIpwd.getPeakProfile(dataType, parmDict, xdata, fixback, varyList, bakType)

Computes the profile for a powder pattern for single peak fitting NB: not used for Rietveld refinement

GSASIIpwd.getPeakProfileDerv(dataType, parmDict, xdata, fixback, varyList, bakType)

Computes the profile derivatives for a powder pattern for single peak fitting

return: np.array([dMdx1,dMdx2,…]) in same order as varylist = backVary,insVary,peakVary order

NB: not used for Rietveld refinement

GSASIIpwd.getPsVoigt(pos, sig, gam, xdata)

Compute the simple Pseudo-Voigt function for a small angle Bragg peak in external Fortran routine

param pos: peak position in degrees param sig: Gaussian variance in centideg^2 param gam: Lorentzian width in centideg

returns: array: calculated peak function at each xdata returns: integral of peak; nominally = 1.0

GSASIIpwd.getWidthsCW(pos, sig, gam, shl)

Compute the peak widths used for computing the range of a peak for constant wavelength data. On low-angle side, 50 FWHM are used, on high-angle side 75 are used, high angle side extended for axial divergence (for peaks above 90 deg, these are reversed.)

Parameters:

• pos – peak position; 2-theta in degrees
• sig – Gaussian peak variance in centideg^2
• gam – Lorentzian peak width in centidegrees
• shl – axial divergence parameter (S+H)/L

Returns:

widths; [Gaussian sigma, Lorentzian gamma] in degrees, and low angle, high angle ends of peak; 20 FWHM & 50 FWHM from position reversed for 2-theta > 90 deg.

GSASIIpwd.getWidthsTOF(pos, alp, bet, sig, gam)

Compute the peak widths used for computing the range of a peak for constant wavelength data. 50 FWHM are used on both sides each extended by exponential coeff.

param pos: peak position; TOF in musec param alp,bet: TOF peak exponential rise & decay parameters param sig: Gaussian peak variance in musec^2 param gam: Lorentzian peak width in musec

returns: widths; [Gaussian sigma, Lornetzian gamma] in musec returns: low TOF, high TOF ends of peak; 50FWHM from position

GSASIIpwd.getdEpsVoigt(pos, alp, bet, sig, gam, xdata)

Compute the double exponential Pseudo-Voigt convolution function derivatives for a neutron TOF & CW pink peak in external Fortran routine

GSASIIpwd.getdFCJVoigt3(pos, sig, gam, shl, xdata)

Compute analytic derivatives the Finger-Cox-Jepcoat modified Pseudo-Voigt function for a CW powder peak

param pos: peak position in degrees param sig: Gaussian variance in centideg^2 param gam: Lorentzian width in centideg param shl: axial divergence parameter (S+H)/L param xdata: array; profile points for peak to be calculated; bounded by 20FWHM to 50FWHM (or vv)

returns: arrays: function and derivatives of pos, sig, gam, & shl

GSASIIpwd.getdPsVoigt(pos, sig, gam, xdata)

Compute the simple Pseudo-Voigt function derivatives for a small angle Bragg peak peak in external Fortran routine

param pos: peak position in degrees param sig: Gaussian variance in centideg^2 param gam: Lorentzian width in centideg

returns: arrays: function and derivatives of pos, sig, gam, & shl

GSASIIpwd.getgamFW(g, s)

Compute total FWHM from Thompson, Cox & Hastings (1987), J. Appl. Cryst. 20, 79-83 lambda fxn needs FWHM for both Gaussian & Lorentzian components

Parameters:

• g – float Lorentzian gamma = FWHM(L)
• s – float Gaussian sig

Returns float:

total FWHM of pseudoVoigt

GSASIIpwd.makeFFTsizeList(nmin=1, nmax=1023, thresh=15)

Provide list of optimal data sizes for FFT calculations

Parameters:

• nmin (int) – minimum data size >= 1
• nmax (int) – maximum data size > nmin
• thresh (int) – maximum prime factor allowed

Returns:

list of data sizes where the maximum prime factor is < thresh

GSASIIpwd.makeMEMfile(data, reflData, MEMtype, DYSNOMIA)

make Dysnomia .mem file of reflection data, etc.

Parameters:

• data (dict) – GSAS-II phase data
• reflData (list) – GSAS-II reflection data
• MEMtype (int) – 1 for neutron data with negative scattering lengths 0 otherwise
• DYSNOMIA (str) – path to dysnomia.exe

GSASIIpwd.makePRFfile(data, MEMtype)

makes Dysnomia .prf control file from Dysnomia GUI controls

Parameters:

• data (dict) – GSAS-II phase data
• MEMtype (int) – 1 for neutron data with negative scattering lengths 0 otherwise

Returns str:

name of Dysnomia control file

class GSASIIpwd.norm_gen(*args, **kwargs)

needs a doc string

GSASIIpwd.peakInstPrmMode = True

Determines the mode used for peak fitting. When peakInstPrmMode=True peak width parameters are computed from the instrument parameters (UVW,… or alpha,… etc) unless the individual parameter is refined. This allows the instrument parameters to be refined. When peakInstPrmMode=False, the instrument parameters are not used and cannot be refined. The default is peakFitMode=True.

GSASIIpwd.setPeakInstPrmMode(normal=True)

Determines the mode used for peak fitting. If normal=True (default) peak width parameters are computed from the instrument parameters unless the individual parameter is refined. If normal=False, peak widths are used as supplied for each peak.

Note that normal=True unless this routine is called. Also, instrument parameters can only be refined with normal=True.

Parameters:normal (bool) – setting to apply to global variable peakInstPrmMode