Use of intensity quotients and differences in absolute structure refinement.
Parsons, Simon; Flack, Howard D.; Wagner, Trixie; Acta crystallographica Section B, Structural science, crystal engineering and materials 69 (2013) 249–259; doi:10.1107/S2052519213010014

data_2311261
_publ_section_title
;
 Use of intensity quotients and differences in absolute structure
 refinement.
;
_journal_issue                   'Pt 3'
_journal_name_full
'Acta crystallographica Section B, Structural science, crystal engineering and materials'
_journal_page_first              249
_journal_page_last               259
_journal_paper_doi               10.1107/S2052519213010014
_journal_volume                  69
_journal_year                    2013
_chemical_formula_sum            'C3 H7 N O2'
_chemical_formula_weight         89.10
_space_group_crystal_system      orthorhombic
_space_group_IT_number           19
_space_group_name_Hall           'P 2ac 2ab'
_space_group_name_H-M_alt        'P 21 21 21'
_atom_sites_solution_hydrogens   difmap
_audit_creation_method           SHELXL-2012
_cell_angle_alpha                90
_cell_angle_beta                 90
_cell_angle_gamma                90
_cell_formula_units_Z            4
_cell_length_a                   5.791(2)
_cell_length_b                   5.944(2)
_cell_length_c                   12.269(2)
_cell_measurement_temperature    100(2)
_cell_volume                     422.3(2)
_computing_structure_refinement  'SHELXL-2012 (Sheldrick, 2012)'
_diffrn_ambient_temperature      100(2)
_diffrn_measured_fraction_theta_full 0.998
_diffrn_measured_fraction_theta_max 0.998
_diffrn_radiation_type           CuK\a
_diffrn_radiation_wavelength     1.54178
_diffrn_reflns_av_R_equivalents  0.0301
_diffrn_reflns_av_unetI/netI     0.0091
_diffrn_reflns_Laue_measured_fraction_full 0.998
_diffrn_reflns_Laue_measured_fraction_max 0.998
_diffrn_reflns_limit_h_max       7
_diffrn_reflns_limit_h_min       -7
_diffrn_reflns_limit_k_max       7
_diffrn_reflns_limit_k_min       -7
_diffrn_reflns_limit_l_max       14
_diffrn_reflns_limit_l_min       -14
_diffrn_reflns_number            19766
_diffrn_reflns_point_group_measured_fraction_full 0.997
_diffrn_reflns_point_group_measured_fraction_max 0.994
_diffrn_reflns_theta_full        67.679
_diffrn_reflns_theta_max         69.074
_diffrn_reflns_theta_min         7.219
_exptl_absorpt_coefficient_mu    1.000
_exptl_crystal_density_diffrn    1.401
_exptl_crystal_F_000             192
_refine_diff_density_max         0.150
_refine_diff_density_min         -0.160
_refine_diff_density_rms         0.039
_refine_ls_abs_structure_details
;
 Flack x determined using 290 quotients [(I+)-(I-)]/[(I+)+(I-)]
 (Parsons and Flack (2004), Acta Cryst. A60, s61).
;
_refine_ls_abs_structure_Flack   0.02(3)
_refine_ls_extinction_coef       0.009(3)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     SHELXL
_refine_ls_goodness_of_fit_ref   1.145
_refine_ls_hydrogen_treatment    refall
_refine_ls_matrix_type           full
_refine_ls_number_parameters     84
_refine_ls_number_reflns         776
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.145
_refine_ls_R_factor_all          0.0217
_refine_ls_R_factor_gt           0.0215
_refine_ls_shift/su_max          0.000
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
;
 w=1/[\s^2^(Fo^2^)+(0.0434P)^2^+0.0353P]
 where P=(Fo^2^+2Fc^2^)/3
;
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0594
_refine_ls_wR_factor_ref         0.0598
_reflns_Friedel_coverage         0.601
_reflns_Friedel_fraction_full    0.997
_reflns_Friedel_fraction_max     0.986
_reflns_number_gt                771
_reflns_number_total             776
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            L_Alanine_B.cif
_cod_data_source_block           L_Alanine_B
_cod_database_code               2311261
_shelxl_version_number           2012-9
_shelx_res_checksum              94832
_shelx_hkl_checksum              37777