Interatomic Potential Model for Molecular Dynamics Simulation of Lithium Borate Melts/Glasses

Abstract

An improved interatomic potential model was proposed for molecular dynamics simulations of lithium borate melt/glass systems. Charge of ion was reconsidered and a new composition dependent ionic charge model was suggested. A new three-body potential model controlling B-O-B angles was also proposed. The three-body term functioned to avoid square network ring consisted of B-O bonds, without preventing the change of boron coordination number between three and four. The edge-shared tetrahedra of four-coordination boron observed in the previous simulation were cleared by applying this three-body potential model.

Figures

Figure 1.

 Schematic view of the undesirable local structure observed in MD results applied 2-body potential model with partial ionic charges for Li₂O-B₂O₃ melt/glasses.

Figure 2.

 Three-body potential, U(θ_BOB, r_OB1, r_OB2)

Figure 3.

 B-O pair correlation function, P_B-O of Li₂O-B₂O₃ system at 500 K.

Figure 4.

 Snapshots of a part of MD cell of 0.33Li₂O-0.67B₂O₃ melt at 1500 K simulated with IA2 model (a) and with IA3 model (b).

Figure 5.

 B-O-B angle distribution in xLi₂O-(1−x) B₂O₃ at 500 K simulated by IA2 model (a) and by IA3 model (b).

Figure 6.

 Ratio of structural units in xLi₂O-(1−x) B₂O₃ at 500 K and ¹¹B NMR results [12].

Figure 7.

 Ring size distribution in xLi₂O-(1−x) B₂O₃ at 500 K simulation applied IA2 (a) and IA3 (b) potential model.

Figure 8.

 Density of xLi₂O-(1−x) B₂O₃ melt/glasses. Open circle and solid circle are simulated by IA2 and IA3, respectively. Squares are the reference data at 298 K [18] and 1129 K [19].

Tables

Table 1. Number of atoms, N in MD cell and charges, z

x	Ntotal	NO	NB	NLi	zO	zB	zLi
0.00	5000	3000	2000	―	−1.2000	1.8000	―
0.10	5016	2926	1881	209	−1.2145	1.7782	1.0
0.20	5014	2834	1744	436	−1.2320	1.7520	1.0
0.33	5005	2695	1540	770	−1.2615	1.7077	1.0
0.40	5019	2629	1434	956	−1.2800	1.6800	1.0

Table 2. Potential parameters

Parameters for the two-body potential terms
element	z		a/nm		b/nm		c/J1/2mol−1/2 nm3
O	−1.2 − 2α		0.1861		0.0151		1.7720
B	1.8 − 3α		0.0723		0.0082		0.0
Li	1.0		0.1110		0.0110		0.1940
pair	D1/MJ mol−1		β1/nm−1		D2/MJ mol−1		β2/nm−1
B-O	120.5582		51.0		−7.3926		22.6
Parameters for the three-body potential terms
relation	f/J	pθ/degree−1		θ0/degree		pr/nm−1		r0/nm
B-O-B	5.0 × 10−4	1.70		100.0		40.00		0.100

Table 3. Ratio, R_u of structural units (%)

		IA2 potential model					IA3 potential model
Temp./K		x					x
		0	0.1	0.2	0.33	0.4	0	0.1	0.2	0.33	0.4
2000	RBIV	2.65	6.06	31.19	12.65	12.34	0.15	2.50	6.65	7.79	5.02
	RBIII	97.20	93.89	68.8	86.95	87.38	99.85	97.45	93.24	92.09	94.85
	RBII	0.15	0.05	0.40	0.38	0.28	0.00	0.05	0.29	0.13	0.14
	ROIII	1.77	2.97	3.88	5.08	4.6	0.10	0.92	1.59	1.60	1.45
	ROII	98.13	90.77	83.27	69.20	62.19	99.90	92.65	85.00	73.84	65.08
	ROI	0.10	6.25	12.77	24.79	32.03	0.00	6.36	13.02	23.34	31.80
	RO0	0.00	0.00	0.07	0.93	1.18	0.00	0.07	0.39	1.22	1.67
1500	RBIV	4.05	11.85	31.19	19.93	20.99	4.09	2.82	6.65	11.56	11.51
	RBIII	95.95	88.14	68.8	80.07	78.94	95.91	97.18	93.24	88.37	88.50
	RBII	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.12	0.06	0.00
	ROIII	2.70	4.72	10.27	5.90	6.62	0.10	0.85	0.88	1.60	1.94
	ROII	97.30	91.05	83.27	71.43	62.42	99.9	92.99	86.94	75.51	67.82
	ROI	0.00	4.24	6.46	22.26	30.35	0.00	6.12	12.10	22.19	28.45
	RO0	0.00	0.00	0.00	0.41	0.61	0.00	0.03	0.07	0.71	1.79
1000	RBIV	6.20	19.04	32.58	41.82	39.27	0.10	3.45	9.64	16.3	19.25
	RBIII	93.80	80.97	67.43	58.18	60.73	99.9	96.55	90.36	83.69	80.76
	RBII	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
	ROIII	4.13	7.38	10.48	11.84	9.43	0.07	1.09	1.80	2.71	1.83
	ROII	95.87	90.33	83.70	71.80	66.76	99.93	92.89	87.12	75.99	71.81
	ROI	0.00	2.29	5.82	16.22	23.24	0.00	6.02	10.9	20.63	25.03
	RO0	0.00	0.00	0.00	0.15	0.57	0.00	0.00	0.18	0.67	1.33
500	RBIV	8.50	22.44	36.81	49.21	51.6	0.35	4.09	11.81	21.30	23.70
	RBIII	91.50	77.57	63.19	50.78	48.40	99.65	95.91	88.19	78.70	76.29
	RBII	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
	ROIII	5.67	9.26	12.1	14.25	13.39	0.23	1.40	2.33	2.67	2.74
	ROII	94.33	88.76	83.06	71.21	65.12	99.77	92.69	87.4	78.89	72.08
	ROI	0.00	1.98	4.83	14.40	20.92	0.00	5.91	10.09	17.81	24.19
	RO0	0.00	0.00	0.00	0.15	0.46	0.00	0.00	0.18	0.63	0.99

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