Structural and dynamical investigation of Mg₂SiO₄ liquid

Abstract

We have numerically studied structure and dynamics in Mg₂SiO₄ liquid. Eight models at pressure up to 40 GPa and at a temperature of 3500 K have been constructed by molecular dynamics simulation. The structural characteristics such as short-, intermediate-range order (denoted as SRO, IRO, respectively) structure and network structure are analyzed via the radial distribution functions, coordination units, bond angle, bond length as well as the number of corner-, edge- and face-sharing bonds and characteristics of all type OT_y linkages. To clarify the dynamical properties, the models at different pressures are relaxed in NVE ensemble for a long time. The diffusivity of the individual atomic species is determined through the dependence of the mean-squared displacement on number of MD steps. Under compression, the local environment around Si and Mg atoms as well as the IRO structure in Mg₂SiO₄ changes significantly. The degree of polymerization of the Si–O network increases with pressure. The Si–O bonds are broken; the Mg atoms tend to incorporate into the Si–O network via both bridging oxygen (BO) and non-bridging oxygen (NBO) to form the –Si–O–Mg– network in Mg₂SiO₄ liquid. In the considered pressure range, the Mg atom always diffuses faster than the O atom and the O atom diffuses faster than the Si atom. The diffusivity of Si, Mg and O atom decreases with increase in pressure.

1 Introduction

Magnesium silicate (MgO–SiO₂) is one of the major planetary materials. Thus, the understanding of its properties under high temperature and pressure conditions is important to understand the interior structure of Earth. Furthermore, magnesium silicate is also an important material in many high technology applications such as porous ceramic membranes for catalytic reactors, biomedical glass and refractory brick. Hence, the knowledge of structure and properties of MgO–SiO₂ in both glass and liquid is necessary to our understanding about the physical and thermal evolution of the Earth as well as controlling the process of material fabrication technology. Therefore, MgO–SiO₂ system has been widely studied by different experiments and simulation methods during the last several years [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. However, experiment is usually difficult to do due to the high melting temperature of MgO–SiO₂ (2163 K ± 25 K [7, 13]). Available experimental results are usually limited to the ambient or low pressure and temperature. Using neutron and X-ray diffraction data with a reverse Monter-Carlo modeling [11,12,13], authors indicated that the mean coordination number (CN) of Mg is 4.5 ± 0.1 and Mg–O bond length (BL) is about 1.99 ± 0.01 Å and 2.21 ± 0.01 Å in MgSiO3 glass. For Mg₂SiO₄ glass, each Si atom links to 4 oxygen to form SiO₄ tetrahedron with the mean Si–O BL of approximately 1.60–1.64 Å. X-ray diffraction study [13] showed that in MgSiO₃ glass, there are two Mg–O BLs at 2.50 Å and four Mg–O BLs at 2.08 Å in the MgO₆ distorted octahedra. Moreover, the mean BL of Mg–O in MgO₄ tetrahedra is 2.04 Å. The Mg–O average CN is 4.5 [9, 14]. However, this value is 5.1 in ref [7, 15] and 5.0 in ref [10]. In Mg₂SiO₄ at 300 K and 0 GPa [10], the Si–O average CN is 4.1, the Si–O and Mg–O BLs are 1.63 and 2.0 Å, respectively.

The nuclear magnetic resonance experiment [16] found that Mg atom is dominant sixfold coordinated and minor fivefold coordinated in both MgSiO₃ and Mg₂SiO₄ systems. Other studies [3, 17] showed that structure of MgSiO₃ consists of MgO_x polyhedra (x = 4, 5, 6) which are linked to the SiO₄ polyhedra by corner-sharing bonds. In situ diffraction studies of magnesium silicate liquid [3] demonstrated the Mg–O BLs in MgO₄ polyhedra are shorter than the one in other MgO_y polyhedra (y = 5, 6). The high proportion of MgO₄ units (68.80%) indicated that the role of Mg can act as a network former in magnesium silicate. Computer simulation can give insight the microstructure and dynamics of multi-component oxide systems as MgO–SiO₂ system. Recently, many simulations of multi-component oxide systems have been focused on investigation of TO_x structural units as well as distribution of linkages between adjacent TO_x [18,19,20,21,22,23]. The structure of MgSiO₃ glass consists of the SiO₄ tetrahedra network which connects to each other via one, two and three bridging oxygens (BO) [18]. The existence of free oxygen (FO) atoms may be the cause of the inhomogeneous of Mg distribution in MgSiO₃ glass [19]. Using MDS, Omar et al. [7] indicated that in Mg₂SiO₄ melts, the CN of Si is mainly four and changes slightly under compression; meanwhile, the CN of Mg increases from five to seven at 24 GPa. The Si–O–Si bond angle decreases as increasing pressure and the IRO structure depend on pressure. Using ab initio MDS for MgSiO₃ melt [24], authors showed the CN of Si significantly increases; meanwhile, the CN of Mg and O almost unchanged with pressure. At ultra-high pressure to 464.7 GPa, the mean CN of Mg, Si and O is about 8.3, 7.3 and 9.9, respectively. In the work [17], the results illustrated the Mg–O BL is about 1.92–1.96 Å. Meanwhile, in Ref [25] the authors indicated the Mg–O BL is about 2.0 Å. The proportion of MgO₄ is dominant (67.4%). Fraction of MgO₅ and MgO₆ is 30.2% and 4.7%, respectively. In other study [26], the results reported that the mean Mg–O BL is about 2.07 Å and MgO₆ units is distorted. For Mg₂SiO₄ forsterite, by first principles simulation, Ghosh et al. [27] showed that at ambient pressure, the Si–O and Mg–O BL are 1.63 and 1.98 Å, respectively. The O–O, Si–Si, Mg–Si and Mg–Mg distances are 2.68, 3.00, 3.19 and 2.92 Å, respectively. The works [4, 28] also studied the local environment of oxygen atoms. The number of FO increases with pressure. In Mg₂SiO₄ liquid at 3000 K, the work [4] showed that the Mg–O and Si–O BL are 1.97 and 1.63 Å, respectively. The Si–O and Mg–O average CN are 4.1 and 5.1, respectively. The viscosity and diffusivity of species of atoms in MgSiO₃ and Mg₂SiO₄ are also indicated in woks [4, 8]. In addition, the structural and chemical local orders as well as degree of polymerization of the Si–O network in silicate glasses and melts can be evaluated by the Qⁿ species. In fact, the mixture of Qⁿ species (n = 1–4) relates directly to different glass properties and to different silicate melt behaviors [9, 10, 13].

This paper serves as the basic knowledge about microstructure and dynamics of Mg₂SiO₄ liquid under compression at atomic level. Furthermore, the structural organization, network structure and degree of polymerization of the silica network in Mg₂SiO₄ liquid are also clarified in detail in this work.

2 Calculation method

The models of Mg₂SiO₄ liquid (3500 K, 0–40 GPa) have been constructed by MDS using periodic boundary condition. The Oganov potential was used in this work [28,29,30,31,32]. The Verlet algorithm was applied to integrate Newton’s equation of motion with the MD step of $\Delta t$ = 0.5 fs. The MD programs were written in C language and executed on Linux operating system. The MD initial configuration is generated by randomly placing all atoms in a simulation box with density of 3.47 g/cm³ [33,34,35]. Next, the model is heated up to 6000 K to remove the effect of remembering initial configuration. Then, the model is cooled down to the temperature of 3500 K at ambient pressure with the cooling rate of about (2.5)10¹² K/s. After that, it relaxed in NPT ensemble (constant pressure and temperature) for a long time (over 10⁶ MD steps) to get the equilibrium sample. From this model, we continue compressing to desired pressure from 5 to 40 GPa and at 3500 K. Finally, these models are relaxed for a long time to reach the equilibrium at constant temperature and pressure for 10⁶–10⁷ MD steps without any disturbance. By this way, we obtained eight models for Mg₂SiO₄ system. The density of Mg₂SiO₄ liquid at ambient pressure is in good agreement with calculated result and experiment in works [33,34,35]. The structural properties of each model are calculated by averaging over 1000 configurations during the last 10⁵ MD steps. To study dynamical properties, the obtained models are relaxed in NVE ensemble (constant volume and energy). The dependence of mean-squared displacement of atoms on MD steps allows to calculate the diffusion coefficient of Si, Mg, O atom via Einstein equation $D = \lim_{t \to \infty } \frac{{r^{2} \left( t \right)}}{6t}$ where <r(t)²> is mean-squared displacement over time t.

3 Results and discussion

3.1 Structural properties

The SRO structure in Mg₂SiO₄ liquid under compression is clarified via analyzing the pair radial distribution functions (PRDF) of Si–O (g_SiO), Mg–O (g_MgO) and O–O (g_OO), distribution of TO_n coordination units (T = Si, Mg), distribution of O–T–O bond angle and T–O BL in TO_n coordination units. The results of the g_SiO and g_MgO at different pressures are shown in Fig. 1. The position of the first peak of g_SiO and g_MgO indicates the Si–O and Mg–O BL, respectively. It can be seen that at 0 GPa, the Si–O, Mg–O and O–O BLs are 1.58, 1.90 and 2.66 Å, respectively. This result is compared with previous experiment and simulation [4, 7, 9, 10, 12, 14, 15, 28] (see Table 1).

Fig. 1

The radial distribution functions of Si–O, Mg–O and O–O pairs at different pressures

Table 1 Comparing r_ij (position of first peak of PRDF g_ij(r)) and Z_ij (the mean coordination number) in Mg₂SiO₄ system at 0 GPa and 3500 K with previous experiment and simulation data

The position of the first peak of g_SiO and g_MgO tends to shift to right with pressure. Meanwhile, the position of the first peak of g_OO displaces strongly to left under compression. This reveals that the average Si–O and Mg–O BLs increase, but the average O–O BLs decrease as the pressure increases. The BLs of Si–O, Mg–O and O–O are 1.60, 1.92 and 2.54 Å, respectively, at 40 GPa. The elongation of the Si–O and Mg–O BL under compression will be explained in detail in the next section. To calculate the CN, we have used the cut-off distance r_Si–O = 2.4 Å and r_Mg–O = 3.02 Å chosen as first minimum after the first peak of the Si–O and Mg–O PRDF, respectively. The mean CN of Mg, Si in Mg₂SiO₄ liquid (3500 K, 0 GPa) is about 4.4 and 4.1 (see Table 1). It can be seen that the CN of Si is in agreement with works [4, 10]. The CN of Mg is consistent with work [9, 12, 14, 28], but the CN of Mg is lower than the one in the work [7, 10, 15]. We clarify the local environment around Si and Mg atoms. The results are shown in Table 2.

Table 2 The percentage of TO_n coordination units (T = Si, Mg) under compression

As can be seen that at ambient pressure, most of Si atoms are surrounded by 4 O atoms to form SiO₄ coordination unit (basic structural unit). Most of Mg atoms are surrounded by 3, 4 and 5 O atoms to form MgO₃, MgO₄ and MgO₅ coordination units, respectively. The fraction of SiO₄, MgO₃, MgO₄ and MgO₅ is 92.2, 14.2, 39.9 and 32.9% in Mg₂SiO₄ liquid at ambient pressure. This fraction decreases as increase in pressure. At higher pressure (40 GPa), most of Si atoms are coordinated by 5 and 6 O atoms, most of Mg atoms are coordinated by 6, 7 and 8 O atoms. The fraction of SiO₅, SiO₆, MgO₆, MgO₇ and MgO₈ coordination units is 46.9, 42.3, 24.7, 41.5 and 24.3%, respectively. This result indicates that the local environment around Si and Mg atoms in Mg₂SiO₄ depends significantly on pressure. According to above analysis, the structure of Mg₂SiO₄ liquid is built by SiO_x (x = 4–6) and MgO_y (y = 3–8) coordination units. These units can be linked to each other through oxygen atoms to form the network structure of Mg₂SiO₄ liquid. By using visualization technique, the SiO_x (x = 4–6) and MgO_y (y = 3–8) network structures in Mg₂SiO₄ liquid are shown in Fig. 2. This result again confirms that the local environment around Si and Mg atoms in Mg₂SiO₄ liquid changes significantly with pressure. Now, we continue clarify the topology of SiO_x and MgO_y coordination units under compression via analyzing distribution of T–O–T bond angles and T–O BLs (T is Si, Mg) that shown in Fig. 3. Figure 3a shows that at ambient pressure, the O–Si–O bond angle distribution in SiO₄ units has a peak at 105°. There is the main peak and a shoulder peak at about at 90° and 160°, respectively, in the distribution of O–Si–O bond angle in SiO₅ units. For SiO₆ units, it has two peaks including the main first peak at 85° and the second small peak at 165°. The O-Si–O bond angle in SiO₅, SiO₆ units is always larger than the one in the SiO₄ units. When pressure compresses to 40 GPa, the distribution of bond angle and bond length for each SiO_x units (x = 4, 5, 6) is almost unchanged with pressures. This indicates the shape of every SiO₄ or SiO₅ or SiO₆ units is identical under compression. Regarding to the distribution of Si–O BL, Fig. 3b indicates that the distribution in SiO₅ and SiO₆ units at ambient pressure is similar to the one at high pressure. However, there is a slight shift to the left of the distribution in SiO₄ units as pressure increases. It means that the size of SiO₅ and SiO₆ units is independent on pressure, but the size of SiO₄ is distorted slightly under compression. The results also show that the Si–O BL in SiO₄ unit is shorter than the one in SiO₅ unit, and the Si–O BL in SiO₆ is the longest. Thus, the elongation of the Si–O BL under compression can be explained as following: when the pressure increases the Si–O coordination number rises to 5, 6. Besides, the shape and size of each SiO₅ or SiO₆ unit are identical and not dependent on pressure. Accordingly, the O–O bond distance decreases, the Coulomb repulsion between O and O goes up. Hence, this leads to elongation of the Si–O BL. Figure 3c and d shows the distribution of Mg–O–Mg bond angles and Mg–O BLs in MgO_x units (x = 3–8). The results show that the shape and size of MgO_x units are slightly dependent on pressures. The MgO_x units are easily more distorted than SiO_x units under compression. Furthermore, most of MgO_x units are MgO₃, MgO₄, MgO₅ units at low pressure and are MgO₆, MgO₇ and MgO₈ at high pressure. Besides, the Mg–O BL in MgO_x units with x = 3–5 is always shorter than the one in MgO_x units with x = 6–8. Namely, the Mg–O BL in MgO₃, MgO₄ and MgO₅ is about 1.90 ± 0.02 Å and in MgO₆, MgO₇ and MgO₈ is about 1.96 ± 0.02 Å. This leads to the average Mg–O BL slightly increases as pressure increases.

Fig. 2

The SiO_x network (a) and MgO_y network (b) at 0 GPa (left) and 40 GPa (right). The SiO₄, SiO₅ and SiO₆ units are in red, black and green colors, respectively. The MgO₃, MgO₄, MgO₅, MgO₆, MgO₇ and MgO₈ units are in green, red, black, navy, pink and blue colors, respectively

Fig. 3

Distribution of O–Si–O and O–Mg–O bond angle (left), Si–O and Mg–O bond length (right) in SiO_x units and MgO_y units, respectively

The IRO structure relates to the radial distribution function of Si–Si (g_Si–Si), Si–Mg (g_Si–Mg) and Mg–Mg (g_Mg–Mg) as well as the distribution of the linkages between two adjacent TO_n units. Figure 4 shows that the position of the first peak of all the PRDF shifts to left as increasing pressure. Namely, the first peak of the g_Si–Si, g_Si–Mg and g_Mg–Mg locates at 3.08, 3.24 and 3.28 Å at ambient pressure and 3.04, 2.92 and 2.78 Å at 40 GPa at high pressure, respectively. Thus, the g_Si–Si, g_Si–Mg and g_Mg–Mg are significantly dependent on pressure. It means that the IRO structure changes significantly under compression. Furthermore, we found that the adjacent TO_n units can be connected by one, two and three sharing oxygen to form the corner-, edge- and face-sharing bonds, respectively (denoted as Csb, Esb and Fsb, respectively). Thus, we calculated the average number of Csb, Esb and Fsb per one unit at various pressures shown in Table 3. The result shows that there is only Csb between the adjacent SiO_x units. The fraction of Esb and Fsb is almost zero. But two adjacent MgO_y units or between two MgO_y and SiO_x units have all Csb, Esb and Fsb. It is clear that at 0 GPa, the Si atom has 0.75 average Csb with other Si atoms. The Si atom has 1.33 average Csb and 0.21 average Esb with Mg atoms. The Mg atom has 2.26 average Csb, 0.74 average Esb and 0.11 average Fsb with other Mg atoms. The average number of all types of links per one structural unit TO_n increases as increasing pressure and in considered pressure range, N_c > N_e > N_f.

Fig. 4

The radial distribution functions of Si–Si, Si–Mg and Mg–Mg pair at different pressures

Table 3 The average number of all types of bonds per one structural unit TO_n

The change of IRO structure in Mg₂SiO₄ liquid is clarified through investigating distribution of oxygen atoms forming types of OT_m linkages in Mg₂SiO₄ liquid (see Fig. 5) as well as the percentage of OT_m coordination units (T = Si, Mg) under compression (see Table 4).

Fig. 5

Distribution of oxygen atoms forming types of OT_m linkages in Mg₂SiO₄ liquid under compression

Table 4 The percentage of OT_m linkages (T = Si, Mg) under compression

The structure of Mg₂SiO₄ units consists of TO_n units which are connected to each other via oxygen atoms to form network structure of system. The network structure of Mg₂SiO₄ liquid is visualized in Fig. 6. It can be seen that the oxygen atoms can be linked to Si and Mg atoms to form OT_m linkages. The fraction (%) of OT_m linkages is described in Table 4, and characteristics of all type of linkages liquid are also shown in detail in Fig. 5. It indicates that at ambient pressure, most of OT_m linkages are OT₃ (45.5%), OT₄ (31.65%) and OT₂ (13.94%). For OT₃ linkages, most of them are Si₂–O–Mg and Si–O–Mg₂; the fraction of OSi₃ and OMg₃ is very small, at nearly 5%. For OT₄ linkages, the proportion of Si–O–Mg₃ accounts for the highest. The fraction of OT_m linkages (m = 2 ÷ 4) decreases, while the fraction of OT_m linkages (m = 5 ÷ 8) increases as increasing pressures. At 40 GPa, most of OT_m linkages are OT₅ (42.72%), OT₆ (24.51%) and OT₄ (23.25%). Most of oxygen link to one Si and four Mg to form Si–O–Mg₄ linkage or link to two Si and three Mg to form Si₂–O–Mg₃ linkage in OT₅ linkages. The Si–O–Mg₅ or Si₂–O–Mg₄ linkages are mainly in OT₆.

Fig. 6

The network structure of Mg₂SiO₄ liquid is at 0 GPa (left) and 40 GPa (right). The Si, O and Mg atoms are red, blue and green color, respectively

The above analysis indicates that the existence of Mg atoms in SiO₂ leads to the Si–O network broken to form most of –Si–O–Mg– network in Mg₂SiO₄ liquid. The Mg atoms tend to incorporate into the Si–O network via both BO and NBO forming most of Si₂–O–Mg, Si–O–Mg₂, Si–O–Mg₃, Si–O–Mg₄, Si₂–O–Mg₃, Si₂–O–Mg₄ and Si–O–Mg₅ linkages. Figure 7 represents the distribution of BO, NBO and FO in Mg₂SiO₄ liquid as a function of pressure, where the BO and NBO denote the O atoms link to at least two Si atoms and only one Si atom, respectively. FO means the O atoms do not link to any Si atoms. It illustrates that there is existence of FO in Mg₂SiO₄ and Mg atoms tend to link with these FO forming O–Mg_y (y = 3–6). The fraction of BO, NBO and FO is 18.7%, 63.4% and 17.9%, respectively, at 0 GPa. The fraction of BO increases, while the figures for NBO and FO have an opposite trend with increase in pressure. At 40 GPa, the proportion of BO, NBO and FO is 38.5%, 50.4% and 11.1%, respectively. Under compression, the Si–O bonds are broken leading to incorporation of Mg atoms into Si–O subnet to forming linkages that O atoms are linked to both Mg and Si atoms at high pressure. We continue to analyze the distribution of BO in SiO_x units to clarify degree of polymerization of the Si–O network in Mg₂SiO₄ liquid. The results are shown in Table 5. For SiO₄ units, there are 112 Si_4-0 units (isolated SiO₄ units), 247 Si_4-1, 198 Si_4-2, 98 Si_4-3 units and 4 Si_4-4 units at ambient pressure. However, the number of Si_4-n drops sharply due to the fraction of SiO₄ units decreases rapidly under compression. Note that Si_4-n means the SiO₄ units with n bridging oxygens. The results also illustrate that most of the SiO₄ units have 1, 2 or 3 BO. For SiO₅ and SiO₆ units, it is clear that the number of Si_5-0 and Si_6-0 (isolated SiO₅ and SiO₆ units) is small. In the considered pressure range, most of SiO₅ units have 2, 3 or 4 BO (87 Si_5-2, 126 Si_5-3 and 103 Si_5-4 at 40 GPa), while most of SiO₆ units have 3, 4 or 5 BO (54 Si_6-3, 92 Si_6-4 and 46 Si_6-5 at 40 GPa).

Fig. 7

Distribution of BO, NBO and FO in Mg₂SiO₄ liquid as a function of pressure

Table 5 Distribution of BO in SiO_x units (x = 4, 5, 6), where Si_x-n denote the SiO_x units with n BO

The number of Si_5-n and Si_6-n increases strongly with pressure. It is easy to understand because the fraction of SiO₅ and SiO₆ units increases under compression and they account for the highest proportion at 40 GPa. The analysis from Fig. 7 and Table 4 indicates that the fraction of BO increase with pressure. Therefore, the degree of polymerization of the Si–O network increases under compression. We found that SiO_x subnets tend to incorporate together to form larger networks that replace isolated subnets and small subnets. This problem is clarified via analysis size distribution of SiO_x subnets at various pressures, shown in Table 6.

Table 6 Distribution of the number of SiO_x subnets and their size at different pressures, where N_s is the number of subnets and N_a is the number of atoms per one subnet (both Si and O)

To calculate size distribution of SiO_x subnets, we do the following: in the set of SiO_x units, all atoms are denoted from 1 to n. If two Si atoms have least one O atom, they will belong to the same subnet and have the same label and the O atoms that link with the Si atom will have the same label with it. Finally, the atoms with the same label will belong to one subnet. The result indicates that the network structure of SiO_x units in the model comprises large subnets, many small subnets and several subnets of isolated SiO_x units. At 0 GPa, it consists of the largest subnets of 424 atoms, three subnets with size from 99 to 126 atoms and many small subnets from several atoms to several dozens of atoms. There are 113 isolated SiO_x units including 109 isolated SiO₅-units and 4 isolated SiO₄-units. At 40 GPa, the largest subnet has 3193 atoms. There are 4 small subnets with 11–21 atoms and 8 isolated SiO₆- and SiO₇-units. The size of the largest subnet increases with pressure. The number of small subnets and isolated SiO_x units decrease. It means that the polymerization of silica network increases under compression.

3.2 Dynamical properties

To clarify the dynamical properties, the models at different pressures are relaxed in NVE ensemble (constant volume and energy) for a long time. The diffusivity of the individual atomic species is determined through calculating the dependence of the mean-squared displacement $r^{2} \left( t \right)$ on the number of MD steps. The diffusion coefficient D of Mg, O and Si is determined by Einstein relation: $D = \lim_{t \to \infty } \frac{{r^{2} \left( t \right)}}{6t}$. The results are shown in Figs. 8 and 9. We find that the dependence of mean-squared displacement is linear function with the number of MD steps. Under compression, the mean-squared displacement of individual atomic species decreases. Therefore, the diffusivity of Mg, Si and O atom decreases with increase in pressure because the polymerization of silica network increases under compression. At 0 GPa, the diffusion coefficient of Si, O and Mg atom is D_Si = 0.346·10⁻⁴, D_O = 0.474·10⁻⁴ and D_Mg = 1.042·10⁻⁴ cm²/s, respectively. The diffusion coefficient of Si, O and Mg atom goes down with pressure. At 40 GPa, D_Si = 0.115·10⁻⁴, D_O = 0.161·10⁻⁴ and D_Mg = 0.215·10⁻⁴ cm²/s. In considered pressure, it shows that D_Mg > D_Si > D_O. It is suitable with the previous simulated results [7, 28]. Thus, the Mg atom diffuses the fastest, and the O atom diffuses faster than the Si atom in Mg₂SiO₄ liquid.

Fig. 8

Time dependence of mean-squared displacement of Si, O and Mg atom at different pressures

Fig. 9

Diffusion coefficient of Si, O and Mg atom at different pressures

4 Conclusions

In this paper, we have presented the studied results for Mg₂SiO₄ system at 3500 K and in the pressure range from 0 to 40 GPa by using MD simulation method. The studied results serve as the basic knowledge about microstructure and dynamics of Mg₂SiO₄ liquid at atomic level under compression. Namely, the structure of Mg₂SiO₄ liquid consists of MgO_y and SiO_x units (x = 4–6, y = 3–8) which are connected to each other via the corner-, edge- and face-sharing bonds to form network structure of system. The average number of all types of bonds per one structural unit TO_n increases with increase in pressure and in the considered pressure range, N_c > N_e > N_f. Under compression, the local environment around Si and Mg atoms as well as the intermediate-range order structure in Mg₂SiO₄ liquid changes significantly. The existence of Mg atoms in SiO₂ leads to the Si–O network broken to form most of –Si–O–Mg– network in Mg₂SiO₄ liquid. The Mg atoms tend to incorporate into the Si–O network via both BO and NBO forming most of Si₂–O–Mg, Si–O–Mg₂, Si–O–Mg₃, Si–O–Mg₄, Si₂–O–Mg₃, Si₂–O–Mg₄ and Si–O–Mg₅ linkages. The network structure of SiO_x units in the model comprises large subnets, many small subnets and several subnets of isolated SiO_x units. The size of the largest subnet increases with pressure. The number of small subnets and isolated SiO_x units decrease. It means that the polymerization of silica network increases under compression. In considered pressure range, we always have D_Mg > D_Si > D_O. The diffusivity of Mg, Si and O atom decreases with increase in pressure due to increase in the polymerization of silica network under compression.