Molecular Dynamics Simulations on Crystal Morphology of N-Guanylurea-dinitramide†

doi:10.7503/cjcu20170363

Abstract

Abstract:

The crystal morphologies of N-guanylurea-dinitramide(FOX-12) under solvent condition were investigated by molecular dynamics simulation with canonical(NVT) ensemble. The FOX-12 surface-solvent molecule adsorption model was constructed to simulate dynamical equilibrium configuration. By calculating the binding energies of solvent and crystal surfaces, the attachment energies in vacuum were modified and the crystal shapes in different solutions were obtained. The FOX-12 crystals were cultivated in H₂O and H₂O/MeOH by natural cooling and characterized by scanning electron microscopy. The results show that the morphologically dominant faces of FOX-12 in vacuum are (110), (200), (201), (011), (002) and (111); the (110) and (011) faces are found to be the morphologically important growth faces in H₂O; the (200) and (011) faces are found to be the morphologically important growth faces in H₂O/MeOH; the predicted crystal morphologies of FOX-12 were in agreement with the experimental results. Furthermore, the radial distribution function(RDF) analyses between H₂O molecules and (110) face of FOX-12 were performed to explore the solvent-crystal interactions.

Key words: N-guanylurea-dinitramide(FOX-12), Crystal morphology, Molecular dynamics simulation, Modified attachment energy model

TrendMD:

LIU Ning, ZHOU Cheng, SHU Yuanjie, WANG Bozhou, WANG Wenliang. Molecular Dynamics Simulations on Crystal Morphology of N-Guanylurea-dinitramide^†[J]. Chem. J. Chinese Universities, 2017, 38(12): 2231.

Figures/Tables 11

Table 1 Comparison of the experimental and optimized lattice parameters of FOX-12

Model	a/nm	b/nm	c/nm	α/(°)	β/(°)	γ/(°)	ρ/(g·cm^-3)
Experimental^[4]	1.367	0.933	0.614	90.00	90.00	90.00	1.775
DREIDING	1.400	0.919	0.615	90.00	90.00	90.00	1.755
Relative error(%)	2.41	-1.50	0.01	0	0	0	-1.13

Fig.1 Unit cell structure of FOX-12

Table 2 Crystal habit parameters of FOX-12 crystal in vacuum predicted by the AE model*

(hkl)	Multiplicity	d_hkl/nm	E_att(total)/ (kJ·mol^-1)	E_att(vdW)/ (kJ·mol^-1)	E_att(H-bond)/ (kJ·mol^-1)	D	R_hkl	Total facet area(%)
(110)	4	0.771	-196.11	-78.44	-117.67	46.85	1.22	33.95
(200)	2	0.683	-161.32	-100.46	-60.86	38.54	1.00	18.27
(201)	2	0.457	-189.20	-128.46	-60.74	45.20	1.17	25.40
(011)	2	0.513	-221.85	-121.14	-100.71	53.00	1.38	14.70
(002)	1	0.307	-205.82	-205.53	-0.29	49.17	1.28	6.42
(111)	4	0.480	-237.76	-119.84	-117.92	56.80	1.47	1.26

Fig.2 Crystal morphology(A) and crystal graph(B) of FOX-12 in vacuum predicted by the AE model

Table 3 Accessible solvent surface area(Aacc) and total crystal face area(Abox) of FOX-12 surfaces calculated by the Connolly surface model

Species	(hkl)
Species	(110)	(200)	(201)	(011)	(002)	(111)
A_acc/nm²	0.5591	0.1485	0	0.2939	0	0
A_box/nm²	11.1434	5.1552	10.0328	11.2639	7.6519	9.1605

Fig.3 Configurations of FOX-12 surface-H2O interfaces from the MD equilibrium (A) (110); (B) (200); (C) (011).

Fig.4 Configurations of FOX-12 surface-H2O/MeOH interfaces from the MD equilibrium (A) (110); (B) (200); (C) (011).

Table 4 Interaction energies, modified attachment energies and relative growth rates of FOX-12 crystal habit faces in solvents

Solvent	(hkl)	E_tot/ (kJ·mol^-1)	E_surf/ (kJ·mol^-1)	E_solv/ (kJ·mol^-1)	E_int/ (kJ·mol^-1)	E_s/ (kJ·mol^-1)	$E' att$ / (kJ·mol^-1)	$R'* hkl$
H₂O	(110)	-31114.1	-29487.9	1862.1	-3488.3	-175.01	-21.10	1.00
	(200)	-28123.8	-26577.8	1630.5	-3176.5	-91.50	-69.82	3.31
	(011)	-31355.9	-29334.1	2183.8	-4205.6	-109.75	-112.10	5.31
H₂O/MeOH	(110)	-27888.6	-29487.9	5890.0	-4290.6	-215.28	19.17
	(200)	-24927.5	-26577.8	5657.9	-4007.7	-115.45	-45.88	1.00
	(011)	-28079.2	-29334.1	6057.7	-4802.8	-125.32	-96.53	2.10

Table 4 Interaction energies, modified attachment energies and relative growth rates of FOX-12 crystal habit faces in solvents

Solvent	(hkl)	E_tot/ (kJ·mol^-1)	E_surf/ (kJ·mol^-1)	E_solv/ (kJ·mol^-1)	E_int/ (kJ·mol^-1)	E_s/ (kJ·mol^-1)	$E' att$ / (kJ·mol^-1)	$R'* hkl$
H₂O	(110)	-31114.1	-29487.9	1862.1	-3488.3	-175.01	-21.10	1.00
	(200)	-28123.8	-26577.8	1630.5	-3176.5	-91.50	-69.82	3.31
	(011)	-31355.9	-29334.1	2183.8	-4205.6	-109.75	-112.10	5.31
H₂O/MeOH	(110)	-27888.6	-29487.9	5890.0	-4290.6	-215.28	19.17
	(200)	-24927.5	-26577.8	5657.9	-4007.7	-115.45	-45.88	1.00
	(011)	-28079.2	-29334.1	6057.7	-4802.8	-125.32	-96.53	2.10

Fig.5 Predicted crystal morphology(A) and SEM image(B) of FOX-12 from H2O

Fig.6 Predicted crystal morphology(A) and SEM image(B) of FOX-12 from H2O/MeOH

Fig.7 RDF analysis of H2O molecules and FOX-12 crystal for the (110) face (A) HFOX-12…OH2O; (B) HH2O…O FOX-12; (C) HH2O…NFOX-12.

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