Table 2. RMSCD, R_{\rm wp}^{{\rm PDF}}, S_{12}^{{\rm PDF}} and r_{\rm p} values for the correct structure (R) and 36 trial structural models (see Table 1 ▸) of barbituric acid in space group P2₁/c .

The S_{12}^{{\rm PDF}} values listed were calculated with a neighbouring range parameter l of 0.5 Å [see equation (7)].

Structural model	RMSCD (Å)	R_{\rm wp}^{{\rm PDF}} (%)	S_{12}^{{\rm PDF}}	r_{\rm p}
R	0.000	21.486	0.9990	0.9769
A1	0.071	33.489	0.9966	0.9438
A5	0.362	77.257	0.9751	0.6887
A10	0.743	86.124	0.9642	0.6012
A15	1.140	94.476	0.9518	0.5186
A20	1.550	92.932	0.9558	0.5420
B1	0.021	25.738	0.9983	0.9666
B5	0.109	54.650	0.9914	0.8425
B10	0.218	65.591	0.9866	0.7742
B15	0.329	70.963	0.9831	0.7373
B20	0.441	72.561	0.9810	0.7202
C01	0.035	24.552	0.9984	0.9697
C05	0.176	47.957	0.9921	0.8823
C10	0.350	68.473	0.9818	0.7568
C15	0.523	76.854	0.9770	0.6841
C20	0.695	78.779	0.9759	0.6707
Beta1	0.028	24.464	0.9986	0.9699
Beta5	0.142	47.097	0.9927	0.8848
Beta10	0.284	64.061	0.9851	0.7837
Beta15	0.425	71.010	0.9813	0.7460
Beta20	0.564	80.066	0.9758	0.6886
P1	0.240	55.200	0.9882	0.8355
P2	0.320	59.309	0.9841	0.8102
P3	0.533	72.550	0.9796	0.7045
P4	0.627	85.219	0.9620	0.6117
P5	0.724	98.093	0.9428	0.5244
O1	0.504	58.540	0.9881	0.8151
O2	0.730	64.151	0.9848	0.7769
O3	0.495	72.649	0.9773	0.7147
O4	0.552	77.677	0.9725	0.6775
O5	0.610	82.078	0.9671	0.6429
PO1	0.217	52.412	0.9905	0.8528
PO2	0.330	71.259	0.9804	0.7153
PO3	0.445	86.359	0.9644	0.5759
PO4	0.483	89.400	0.9544	0.5456
PO5	0.525	92.599	0.9331	0.5177
W	1.940	109.842	0.8947	0.4242