[dc02af0] | 1 | r""" |
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[a5d0d00] | 2 | This model provides the scattering intensity, $I(q) = P(q) S(q)$, for a |
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| 3 | lamellar phase where a random distribution in solution are assumed. |
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[eb69cce] | 4 | Here a Caille $S(q)$ is used for the lamellar stacks. |
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| 5 | |
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| 6 | Definition |
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| 7 | ---------- |
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[dc02af0] | 8 | |
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[a5d0d00] | 9 | The scattering intensity $I(q)$ is |
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[dc02af0] | 10 | |
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[eb69cce] | 11 | .. math:: |
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[a5d0d00] | 12 | |
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[6ab4ed8] | 13 | I(q) = 2\pi \frac{P(q)S(q)}{q^2\delta } |
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[dc02af0] | 14 | |
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| 15 | The form factor is |
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| 16 | |
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[eb69cce] | 17 | .. math:: |
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[a5d0d00] | 18 | |
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| 19 | P(q) = \frac{2\Delta\rho^2}{q^2}\left(1-\cos q\delta \right) |
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[dc02af0] | 20 | |
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| 21 | and the structure factor is |
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| 22 | |
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[eb69cce] | 23 | .. math:: |
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[a5d0d00] | 24 | |
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| 25 | S(q) = 1 + 2 \sum_1^{N-1}\left(1-\frac{n}{N}\right) |
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| 26 | \cos(qdn)\exp\left(-\frac{2q^2d^2\alpha(n)}{2}\right) |
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[dc02af0] | 27 | |
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| 28 | where |
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| 29 | |
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[eb69cce] | 30 | .. math:: |
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[d18f8a8] | 31 | :nowrap: |
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[dc02af0] | 32 | |
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[d18f8a8] | 33 | \begin{align*} |
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[eb69cce] | 34 | \alpha(n) &= \frac{\eta_{cp}}{4\pi^2} \left(\ln(\pi n)+\gamma_E\right) |
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[d18f8a8] | 35 | && \\ |
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[eb69cce] | 36 | \gamma_E &= 0.5772156649 |
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[d18f8a8] | 37 | && \text{Euler's constant} \\ |
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[eb69cce] | 38 | \eta_{cp} &= \frac{q_o^2k_B T}{8\pi\sqrt{K\overline{B}}} |
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[d18f8a8] | 39 | && \text{Caille constant} |
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| 40 | \end{align*} |
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[dc02af0] | 41 | |
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[7c57861] | 42 | Here $d$ = (repeat) d_spacing, $\delta$ = bilayer thickness, |
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[a5d0d00] | 43 | the contrast $\Delta\rho$ = SLD(headgroup) - SLD(solvent), |
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| 44 | $K$ = smectic bending elasticity, $B$ = compression modulus, and |
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| 45 | $N$ = number of lamellar plates (*n_plates*). |
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[dc02af0] | 46 | |
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[a5d0d00] | 47 | NB: **When the Caille parameter is greater than approximately 0.8 to 1.0, the |
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| 48 | assumptions of the model are incorrect.** And due to a complication of the |
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| 49 | model function, users are responsible for making sure that all the assumptions |
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| 50 | are handled accurately (see the original reference below for more details). |
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[dc02af0] | 51 | |
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[a5d0d00] | 52 | Non-integer numbers of stacks are calculated as a linear combination of |
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| 53 | results for the next lower and higher values. |
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| 54 | |
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| 55 | The 2D scattering intensity is calculated in the same way as 1D, where the |
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| 56 | $q$ vector is defined as |
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[dc02af0] | 57 | |
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| 58 | .. math:: |
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| 59 | |
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[a5d0d00] | 60 | q = \sqrt{q_x^2 + q_y^2} |
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[dc02af0] | 61 | |
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| 62 | |
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[0507e09] | 63 | |
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[eb69cce] | 64 | References |
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| 65 | ---------- |
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[dc02af0] | 66 | |
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[0507e09] | 67 | .. [#] F Nallet, R Laversanne, and D Roux, *J. Phys. II France*, 3, (1993) 487-502 |
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| 68 | .. [#] J Berghausen, J Zipfel, P Lindner, W Richtering, *J. Phys. Chem. B*, 105, (2001) 11081-11088 |
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| 69 | |
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| 70 | Source |
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| 71 | ------ |
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| 72 | |
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| 73 | `lamellar_stack_caille.py <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/lamellar_stack_caille.py>`_ |
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| 74 | |
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| 75 | `lamellar_stack_caille.c <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/lamellar_stack_caille.c>`_ |
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| 76 | |
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| 77 | Authorship and Verification |
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| 78 | ---------------------------- |
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[dc02af0] | 79 | |
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[0507e09] | 80 | * **Author:** |
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| 81 | * **Last Modified by:** |
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| 82 | * **Last Reviewed by:** |
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| 83 | * **Source added by :** Steve King **Date:** March 25, 2019 |
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[dc02af0] | 84 | """ |
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[2d81cfe] | 85 | |
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| 86 | import numpy as np |
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[3c56da87] | 87 | from numpy import inf |
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[dc02af0] | 88 | |
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[6ab4ed8] | 89 | name = "lamellar_stack_caille" |
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[dc02af0] | 90 | title = "Random lamellar sheet with Caille structure factor" |
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| 91 | description = """\ |
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[ec2ca99] | 92 | [Random lamellar phase with Caille structure factor] |
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| 93 | randomly oriented stacks of infinite sheets |
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| 94 | with Caille S(Q), having polydisperse spacing. |
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| 95 | sld = sheet scattering length density |
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| 96 | sld_solvent = solvent scattering length density |
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| 97 | background = incoherent background |
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| 98 | scale = scale factor |
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[dc02af0] | 99 | """ |
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[a5d0d00] | 100 | category = "shape:lamellae" |
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[dc02af0] | 101 | |
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[7f1ee79] | 102 | single = False # TODO: check |
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[ec2ca99] | 103 | # pylint: disable=bad-whitespace, line-too-long |
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[3e428ec] | 104 | # ["name", "units", default, [lower, upper], "type","description"], |
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[ec2ca99] | 105 | parameters = [ |
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| 106 | ["thickness", "Ang", 30.0, [0, inf], "volume", "sheet thickness"], |
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[a57b31d] | 107 | ["Nlayers", "", 20, [1, inf], "", "Number of layers"], |
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[7c57861] | 108 | ["d_spacing", "Ang", 400., [0.0,inf], "volume", "lamellar d-spacing of Caille S(Q)"], |
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[ec2ca99] | 109 | ["Caille_parameter", "1/Ang^2", 0.1, [0.0,0.8], "", "Caille parameter"], |
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[42356c8] | 110 | ["sld", "1e-6/Ang^2", 6.3, [-inf,inf], "sld", "layer scattering length density"], |
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| 111 | ["sld_solvent", "1e-6/Ang^2", 1.0, [-inf,inf], "sld", "Solvent scattering length density"], |
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[ec2ca99] | 112 | ] |
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| 113 | # pylint: enable=bad-whitespace, line-too-long |
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[3e428ec] | 114 | |
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[0bef47b] | 115 | source = ["lamellar_stack_caille.c"] |
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[dc02af0] | 116 | |
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[404ebbd] | 117 | def random(): |
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[b297ba9] | 118 | """Return a random parameter set for the model.""" |
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[404ebbd] | 119 | total_thickness = 10**np.random.uniform(2, 4.7) |
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| 120 | Nlayers = np.random.randint(2, 200) |
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| 121 | d_spacing = total_thickness / Nlayers |
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| 122 | thickness = d_spacing * np.random.uniform(0, 1) |
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| 123 | Caille_parameter = np.random.uniform(0, 0.8) |
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| 124 | pars = dict( |
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| 125 | thickness=thickness, |
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| 126 | Nlayers=Nlayers, |
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| 127 | d_spacing=d_spacing, |
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| 128 | Caille_parameter=Caille_parameter, |
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| 129 | ) |
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| 130 | return pars |
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| 131 | |
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[dc02af0] | 132 | # No volume normalization despite having a volume parameter |
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| 133 | # This should perhaps be volume normalized? |
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| 134 | form_volume = """ |
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| 135 | return 1.0; |
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| 136 | """ |
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| 137 | |
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[3e428ec] | 138 | demo = dict(scale=1, background=0, |
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[7c57861] | 139 | thickness=67., Nlayers=3.75, d_spacing=200., |
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[6ab4ed8] | 140 | Caille_parameter=0.268, sld=1.0, sld_solvent=6.34, |
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[ec2ca99] | 141 | thickness_pd=0.1, thickness_pd_n=100, |
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[7c57861] | 142 | d_spacing_pd=0.05, d_spacing_pd_n=40) |
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[dc02af0] | 143 | |
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[7f47777] | 144 | # |
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| 145 | tests = [ |
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[ec2ca99] | 146 | [{'scale': 1.0, 'background': 0.0, 'thickness': 30., 'Nlayers': 20.0, |
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[7c57861] | 147 | 'd_spacing': 400., 'Caille_parameter': 0.1, 'sld': 6.3, |
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| 148 | 'sld_solvent': 1.0, 'thickness_pd': 0.0, 'd_spacing_pd': 0.0}, |
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[ec2ca99] | 149 | [0.001], [28895.13397]] |
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| 150 | ] |
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[40a87fa] | 151 | # ADDED by: RKH ON: 18Mar2016 converted from sasview previously, now renaming everything & sorting the docs |
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