Revisiting the Structural, Electronic, and Magnetic Properties of (LaO)MnAs: Effect of Hubbard Correction and Origin of Mott-Insulating Behavior.

We study the structural, electronic, and magnetic properties of the antiferromagnetic-layered oxyarsenide (LaO)MnAs system from the first-principle calculation. The increasing Hubbard energy (U) in the Mn 3d orbital induces the increasing local-symmetry distortions (LSDs) in MnAs4 and OLa4 tetrahedra. The LSD in MnAs4 tetrahedra is possibly promoted by the second-order Jahn-Teller effect in the Mn 3d orbital. Furthermore, the increasing U also escalates the bandgap (E g) and the magnetic moment of Mn (μMn). The value of U = 1 eV is the most appropriate by considering the structural properties. This value leads to E g and μMn of 0.834 eV and 4.31 μB, respectively. The calculated μMn is lower than the theoretical value for the high-spin state of Mn 3d (5 μB) due to the hybridization between Mn 3d and As 4p states. However, d xy states are localized and show the weakest hybridization with valence As 4p states. The Mott-insulating behavior in the system is characterized by the E g transition between the valence and conduction d zx /d zy states. This work shows new physical insights for advanced functional device applications, such as spintronics.

Introduction

Layered oxypnictides (LaO)TPn (T = transition metals, Pn = P, As, Sb) have been extensively investigated because of their various properties. Doping F in (LaO)FeAs induces the superconducting behavior with the high Curie temperature (TC).[1] (LaO)NiAs exhibits the strong-coupling superconducting behavior with the enhanced TC by F substitutional doping at O sites.[2] Behaving as the itinerant ferromagnetic material, (LaO)CoAs exhibits the possible crossover of 3D-to-2D fluctuations above 150 K.[3] (LaO)ZnPn (Pn = P, As, Sb) shows the semiconducting behavior, where its structural, electric, and electronic properties are strongly dependent on Pn substitution.[4] It has been found that (LaO)ZnP shows diamagnetism, while (LaO)ZnAs and (LaO)ZnSb show paramagnetism.[5] (LaO)MnPn (Pn = P, As, Sb) exhibits the insulating behavior based on the temperature (T)-dependent electrical resistivity (4–300 K).[6]

As one of the manganese-based layered oxypnictides, the (LaO)MnAs system consists of [LaO] and [MnAs] layers stacked along the c-axis direction with the space group P4/nmm. As (La) ions tetrahedrally surround Mn (O) ions, this leads to LaMn4 and OLa4 tetrahedra. [LaO] layers show the covalent bonding between La and O atoms, while [MnAs] layers show the ionic bonding between Mn and As atoms based on the synchrotron X-ray powder diffraction (SXRD) measurement and the first-principle calculation.[7] At room temperature (RT), doping holes into [MnAs] layers changes the antiferromagnetic insulating to ferromagnetic metallic behaviors. The doping was performed by inducing defects in [LaO] layers. Achieving x = 0.3, the (LaO)1–MnAs system exhibits the metallic behavior for T < 150 K.[6] The (LaO)MnAs system shows interesting properties. It exhibits the giant negative magnetoresistance up to −24% at 200 K[8] as well as the G-type antiferromagnetic behavior[9] with the Néel temperature (TN) above RT, which is 360(1) K.[10] In the system, Mn 3d spins aligned ferromagnetically along the c axis and antiferromagnetically along the ab plane based on the neutron diffraction measurement.[9] The (LaO)MnAs system also exhibits the Mott-insulating behavior,[11] which is partly contributed by the superexchange interaction between Mn and As ions.[7] The Mott-insulating behavior is related to the half-filled d orbital (d5) in the system.[12] The previous first-principle calculation has shown that the insulating behavior is strongly correlated by the G-type magnetism at the ground state, while the metallic behavior is correlated with the ferromagnetic state. The insulating or semiconductor behaviors are indicated by the bandgap (Eg) transition, which is mainly contributed by the valence and conduction Mn 3d states.

In the electronic properties of (LaO)MnAs, the conventional density-functional theory (DFT) provides the underestimated Eg. The Hubbard energy (U) correction can be carried out to correct the electronic properties. The term U is significant in changing Eg and moment magnetic of Mn ion (μMn). The previous calculation shows that Eg of the (LaO)MnAs system is increased by the U–J value and saturates for U–J more than 4 eV, which is large enough for the Mn 3d orbital.[13] The term U can also correct the magnetic properties in terms of spin-state assignments in Mn 3d and structural properties.[14] Using the local density approximation (LDA) + U method, the previous investigation shows that the value of U = 2 eV for Mn 3d gives the consistent crystal volume structures of the Pr0.75Na0.25MnO3 system compared to the experimental data.[15] For the same system, the change in U value for Mn 3d also significantly influences the crystal structure, electronic properties, the charge and spin densities, and the hybridization of Mn 3d and O 2p orbitals.[16]

As the (LaO)MnAs system shows the antiferromagnetic semiconducting behaviors, it is expected to be suitable for spintronic application. The antiferromagnetic semiconductors are suggested to be promising for spintronics since these semiconductors provide the higher magnetic ordering temperature than the diluted magnetic semiconductors.[17] Furthermore, the semiconductor behavior in an antiferromagnetic material can be used for measuring the anisotropic magnetoresistance. Alongside the electrical resistance measurement, they provide the charge and spin-dependent transport for spintronics.[18] Furthermore, the antiferromagnetic behavior is suggested to be suitable for spintronic applications since the materials show no parasitic magnetic fields. The antiferromagnetic materials exhibit the fast antiferromagnetic state switching and are insensible under external magnetic fields. The semiconducting behavior provides Eg, which is suitable for applications in electronic devices.[19] Regarding the structural properties, the local-symmetry distortion (LSD) in MnAs4 and OLa4 tetrahedra has not been explored yet. Moreover, the contribution of orbital states to the antiferromagnetic insulating behaviors is yet to be explored. For instance, the role of sub-Mn 3d states to the behaviors is not clear despite the remarkable contribution of Mn 3d states.

In this paper, we study the structural, electronic, and magnetic properties of the (LaO)MnAs system, calculated by first principles based on the density-functional theory (DFT). The structural properties are systematically investigated, which include the LSD in both MnAs4 and OLa4 tetrahedra. Then, the electronic and magnetic properties are discussed in terms of the band structure and magnetic moment at Mn sites. Finally, energy-dependent total and projected density of states (DOS) are revealed to find the electronic properties of each orbital in the system.

Calculation Details

The Quantum ESPRESSO code[20] was employed to calculate the structural and electronic properties of (LaO)MnAs with the space group of P4/nmm (no. 129).[21]Figure visualizes the crystal structure model of the systems, which shows MniAs4 (i = 1, 2) and OLa4 tetrahedra and is modeled using VESTA.[22] All-electron potentials are implemented by the ultrasoft pseudopotentials within the Vanderbilt scheme.[23] The calculation carried out the plane-wave method within the generalized gradient approximation (GGA) employing the Perdew–Burke–Ernzerhof (PBE)-type exchange–correlation functional energy.[24] The properties of various systems have previously been calculated using this method.,[4b][25] As the initial magnetic state, the magnetic orders of Mn1 and Mn2 are antiferromagnetic along the ab plane and ferromagnetic along the c axis directions.[8] The present work employed the initial structural properties of a = 4.11920 Å, c = 9.04312 Å, zLa = 0.13247, and zAs = 0.66879 from our previous report.[7] First, using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm,[26] a full optimization of structural properties was performed with a threshold force of 10–3 Ry/Bohr (∼0.03 eV/Å). Using the Broyden mixing scheme,[27] the self-consistent-field (SCF) calculation carried out a threshold energy, cut-off kinetic energy, and k-point mesh of 10–4 Hartree (∼2.72 × 10–3 eV), 60 Rydberg (∼816 eV), and 9 × 9 × 4, respectively. Then, the band structures were calculated within a k-point path of M-A-Z-Γ-X-M-Γ in the corresponding Brillouin zone as previously carried out for (LaO)ZnAs.[4b] The corresponding non-self-consistent-field (NSCF) calculation was performed to generate a spin-polarized total and projected DOS using the doubled k-point mesh of 18 × 18 × 8. The on-site Coulomb repulsion energy or Hubbard energy (U)[28] was used for the Mn 3d orbital with a U of 0–10 eV with an increment of 1 eV.

Figure 1

Crystal structures of the (LaO)MnAs system. Blue and red shades denote ZnPn4 and OLa4 tetrahedra. The up (↑) and down arrows (↓) represent initial magnetic alignment at Mn1 and Mn2 sites, respectively.

Results and Discussion

Structural Properties

Figure a shows the U dependences of a and c compared to that of the previous experiment.[7] The increase in U induces the increase in a and c with the decreasing of the gradients Δa/ΔU and Δc/ΔU. It is found that the values of U = 1 and 0 eV respectively induce the closest a and c to those of the previous report. The result also shows that c is more sensitive to the change of U than a. The increments of a and c have also been obtained in the rutile and anatase TiO2 systems with the tetragonal crystal structure. It is well known that the term U expands their unit cell volume.,[25a][29] However, the increments of a and c of the rutile TiO2 system are almost linear, which are in contrast to that of the (LaO)MnAs system in the present work.[25a]Figure b shows the U dependences of the ratio c/a. The increase in U from 0 to 1 eV promotes the sharp decrease in c/a. For 1 < U < 4 eV, c/a is decreased with the minimum value at U = 3 eV and then reaches its maximum at U = 4 eV. For U > 4 eV, c/a is decreased with the sharper gradient than that of the range of 1 < U < 3 eV. We find that c/a is in a good agreement with that of the experiment for U = 6 eV. However, this value is too large for the Mn site. The present work does not consider the effect of U of the La 4f orbital since its presence has no effect in changing Eg.[13] Therefore, the term U of La 4f is negligible. Figure c presents the U dependences of the c-axis coordinate of La (zLa) and As atoms (zAs). The value of U = 1 eV induces the closest zLa and As atoms zAs to those of the previous report. This result shows the increasing thickness of [MnAs] layers since both c and zAs increase due to the U increment. Furthermore, one can assume that the Mn 3d orbital should not have a very large U value in the system.

Figure 2

Hubbard energy (U) dependences of (a) lattice parameters (a, c), (b) ratio c/a, and (b) c-axis coordinate of La and As atoms (zLa, zAs) in the (LaO)MnAs system compared to those of the previous experiment.

Based on Figure , bond lengths and bond angles in the (LaO)MnAs system are presented in Figure . Figure a presents the U dependences of bond lengths between La and O sites (lLa–O) as well as between La and As sites (lLa–As). It is shown that the increase in U induces the increase in lLa–O and lLa–As with the decreasing of the gradients ΔlLa – O/ΔU and ΔlLa – As/ΔU. The increasing lLa–O and lLa–As are in line with the increases in a and c. It is found that lLa–O and lLa–As are close to the experimental results for U = 1 and 2 eV, respectively. Figure b shows the U dependences of bond length between Mn and As sites (lMn–As). The increase in U induces the increase in lMn–As with the decreasing of the gradient ΔlMn – As/ΔU. The value of U = 1 eV induces the closest lMn–As to that of the experiment. Figure c shows the U dependences of bond angle between La and O sites (θO–La–O) as well as As sites (θAs–La–As). Centered at Mn sites, two bond angles between Mn and As sites (θAs–Mn–As), which are α and β, are also presented as the function of U in Figure d. The increase in U induces the increase in θO–La–O, θAs–La–As, and β, while α is decreased. The value of U = 1 eV promotes the closest θO–La–O, α, and β to that of the experiment, while θAs–La–As is close to the experimental result for U = 2 eV.

Figure 3

Hubbard energy (U) dependences of (a) bond length (l) of La–O, La–As, and (b) Mn–As bonds. Bond angles of (c) O–La–O, As–La–As, and (d) As–Mn–As (α, β) are also presented.

Based on Figure , the local-symmetry distortion (LSD) in MnAs4 and OLa4 tetrahedra shifts with the increase in U. For quantitatively describing the LSD, we carry out the LSD parameters.[30] For the tetrahedron AX4, the first LSD parameter is the mean quadratic elongation (λtet) formulated aswhere l0 is the A–X bond length for an ideal AX4 tetrahedron with the same volume as that of the distorted tetrahedron and l is A–X bond lengths. The second parameter is the bond-angle variance (θtet2), expressed aswhere θ is the X–A–X bond angles.[30a] Notably, the bond angle 109.4712° is possessed by the ideal tetrahedron.[31] In the present work, both parameters are used for both MnAs4 and OLa4 tetrahedra as shown in Figure . Figure a shows that λtet of OLa4 is larger than that of MnAs4 for each U value. Figure b also depicts that θtet2 of OLa4 is larger than that of MnAs4 for each U value. The increase in U induces the increases in λtet and θtet2. The LSD possibly comes from the second-order Jahn–Teller (JT) effect since the 3d5 orbital cannot possess the first-order Jahn–Teller effect. This possible mechanism has been suggested in our previous reports.,[4b][32]

Figure 4

Hubbard energy (U) dependences of (a) mean quadratic elongation and (b) bond angle variance in (c) MnAs4 and (d) OLa4 tetrahedra.

From the structural properties, the value of U = 1 eV is the most suitable value for the system in the present work. This value is used to discuss the electronic properties. Notably, this value induces the different result with that of previous experimental reports. However, this value is sufficient to obtain the closest structural properties to that of previous experiments. The next subsection will show more details regarding this issue.

Band Structures

Figure a shows the U dependence of indirect Eg of the (LaO)MnAs system, compared to that of the previous experiment, that is E ≈ 1.4 eV.[33] Since the system exhibits the antiferromagnetic behavior, spin-up and spin-down band structures have the same profile based on the calculation result. Then, we only present the band structure for a single spin orientation. The present work shows the maximum Eg because of the wider range in sweeping Eg. The inset shows the band structure for U = 0 eV. We find the indirect Eg transition from the Γ to M point, which is in line with that of the previous calculation.[33] This transition is used to show the trend of Eg. The result depicts that the increase in U induces the increase in Eg with the maximum value at U = 8 eV (Eg = 1.348 eV) and the slight decrease in Eg for 8 < U ≤ 10 eV. Although the value of U = 8 eV results in the closest Eg to that of the previous experiment, this U value induces the overestimated lattice parameters as shown in Figure . The increase in Eg is in alignment with that of the previous calculation, showing the saturation at U of 4 eV with the U range of 0–5 eV.[13] Instead of depicting a saturation feature, the present work shows the maximum Eg because of the wider range in sweeping Eg. On the other hand, for U = 1 eV, we find an Eg of 0.834 eV, which is ∼60% of the experimental result. The value of U = 1 eV is more reasonable since it is the most suitable value for the structural properties. Moreover, the underestimated Eg is acceptable because of the limitation of the GGA method in describing Eg in the electronic properties.[34] Furthermore, the previous report shows that the small value of U = 2 eV for Mn 3d can give the suitable crystal volume structures of the Pr0.75Na0.25MnO3 system compared to the experimental data.[17]

Figure 5

Hubbard energy (U) dependences of (a) indirect bandgap (Eg) (between Γ and M points) and (b) magnetic moment of Mn. Insets in (a) and (b) respectively show the band structure of (LaO)MnAs for U = 0 eV and spin configurations for high and spin states. The up (↑) and down arrows (↓) denote the spin-up and spin-down electrons, respectively.

Figure b presents the U dependence of μMn in the (LaO)MnAs system. The increase in U induces the increase in μMn. We suggest that the increase in μMn might be influenced by the increase in LSD relating to the increasing the second-order JT effect in the Mn2+ case. This suggestion is based on the increasing μMn due to the JT effect in the LaMnO3 system. This suggestion will be elaborated in a future publication. However, for all U, μMn values are higher than those of the previous experimental report, which is 3.34(2) μB.[9] For U = 1 eV, we find a μMn of 4.31 μB, which is close to that of the other experimental report, i.e., ∼4.00 μB at low T.[35] From the theoretical point of view, Mn2+ ion has the electron configuration of [Ar] 3d54s0, leading to the theoretical magnetic moment of 5 μB with the high-spin (HS) state (S = 5/2, t23e2). For the case of smaller tetrahedral crystal-field splitting energy (Δt) between e and t2 states than pairing energy between spins, only HS states are possible to exist in the 3d orbital. However, the low-spin (LS) state (S = 1/2, t24e1) can possibly exist in the tetrahedral coordination with a sufficiently large Δt.[36] The spin configurations of HS and LS states are illustrated in the inset of Figure b. For the Mn 3d orbital, as the counterpart of the HS state, the LS state can possibly exist for sufficiently large Δt. It might be suggested that in the present work, the Mn 3d orbital exhibits the mixed HS–LS state, where the HS state portion is more pronounced for the higher U. Furthermore, the interaction between spins in the Mn 3d orbital can be considered into two possibilities. First, the interaction can be affected by the direct exchange between the nearest-neighboring Mn ions. Second, the interaction can be contributed by the superexchange with As ions. By extracting from Figure , we obtain lMn–Mn of 2.92184 and 2.91271 Å for U = 1 eV and from the previous experiment.[7] On the other hand, the body-centered cubic (bcc) δ−Mn and the face-centered cubic (fcc) γ–Mn crystals show lMn–Mn of 2.66822 and 2.73155 Å between the nearest-neighboring Mn sites.[37] These values imply that the direct exchange between Mn ions is not dominant in the (LaO)MnAs system. The superexchange between Mn and As ions may provide the dominant contribution to the spin state. This suggestion is supported by the previous report suggesting that a lower μMn than 5 μB can be promoted by the substantial hybridization of As 4p and Mn 3d orbitals.[9] We will clarify this suggestion in Section .

Projected Density of States

Figure a shows the total DOS of the (LaO)MnAs system for spin-up and spin-down orientations for U = 1 eV. In the approximate range of −5 to −3 eV, we find a large DOS peak for each spin orientation with a ripple feature. For the approximate range from −3 to −0.5 eV, two lower valence band peaks are shown near EF. Above EF, the result shows the conduction band in the approximate range from 0.4 to 2.5 eV with the two highest peaks at around 1.5 and 2.4 eV. The absence of state between the valence and conduction bands indicates Eg shown in Figure a. For describing states contributing to both valence and conduction bands, we further present the projected DOS of orbitals involved in the system.

Figure 6

(a) Total density of states (DOS) of the (LaO)MnAs system. (b) Projected DOS of La 5d, La 4f, and O 2p, and (c) Mni 3d (i = 1, 2) are also presented. In (c), DOS summation of Mn1 3d and Mn2 3d states is presented in the dashed line. Spin-up and spin-down states are denoted by ↑ and ↓, respectively. Notably, the value of U = 1 eV is used.

The projected DOS data are presented in Figure b,c. Figure b shows the projected DOS of La 5d, La 4f, and O 2p states. We find that La 5d and O 2p states are deeply located in the valence band at around −4 eV. With the deep separation between both states and Fermi level (EF), electrons in [LaO]+ layers are difficult to excite to the conduction band. On the other hand, La 4f states are localized at 2.4 eV, indicating that the La 4f orbital is empty. This result leads to an insulating behavior in these layers. Furthermore, the presence of insulating [LaO]+, as well as the conducting [MnAs]− layers indicated by the capability of electrons to be excited from the valence to the conduction bands through Eg (see Figure c), shows that the (LaO)MnAs system is a natural superlattice. Some layered systems reported as the natural superlattice show the potential application for the thermoelectric power.,[25c][38] However, we do not find any reference showing any evidence of potential application for thermoelectricity. Figure c shows the projected DOS of Mni 3d (i = 1, 2) and As 4p states. The valence Mn1 3d and Mn3 3d states contribute to the large DOS peak at around −4 eV. Above them, Mn1 3d and Mn2 3d states contribute to the lower peaks, which hybridize with As 4p states. Our results are in line with the valence-band photoemission (PE) spectrum reported by Higashiya et al. The measurement was performed using X-ray photoelectron spectroscopy (XPS) with a horizontally polarized X-ray photon energy of 7.9 keV. The PE spectrum of (LaO)MnAs indicates that O 2p states and Mn 3d states are located at around −5 eV. On the other hand, Mn 3d states hybridize with As 4p states and contribute to the region between −3.5 eV and EF.[39]

From Figure c, the conduction band shows that Mn1 3d and Mn2 3d states dominate from 0.4 to 2.0 eV. The result shows that the conduction band minimum (CBM) and valence band maximum (VBM) mainly come from Mn 3d and As 4p states. It is shown that, at the VBM, the portion of Mn 3d and As 4p states is almost the same, indicating that Eg transition can occur from between Mn 3d states. This result pronounces the Mott insulator characteristics.[11b] We suggest that the presence of As 4p states at around VBM is induced by their strong hybridization with Mn 3d. This result supports our suggestion in the previous subsection that the lower μMn can be induced by the hybridization between Mn 3d and As 4p states.[9] Furthermore, the DOS shape of Mn2 3d has the mirrored shape of the DOS shape of Mn1 3d states, showing the antiferromagnetic behavior localized at Mn1 and Mn2 sites. It is remarkably shown that for the Mn1 site, all the spin-up and spin-down Mn1 3d states are almost located at the valence and conduction bands, respectively. This feature indicates that all sub-Mn1 3d orbitals are occupied by five spin-up electrons, depicting the HS state. For the same reason, all sub-Mn2 3d orbitals are occupied by five spin-down electrons as the result of the G-type antiferromagnetic ordering of Mn2+ ions.[13] In the range of −2.5 to −0.5 eV, both spin-up and sub-Mn 3d orbital is occupied, indicating a very small contribution of LS state due to the strong hybridization between both spin Mn 3d and As 4p states. This result confirms the previous suggestion that the spin state in the Mn 3d orbital is mainly contributed by the superexchange between Mn and As ions. However, the presence of both the occupied sub-Mn 3d orbital might also imply the Mn oxidation state of 3+. We suggest that the possible oxidation state corresponds to a theoretical μMn of 4 μB for the HS state (S = 2) of the Mn3+ 3d4 orbital and close to the calculated μMn for small U. This suggestion follows the simple rules for the Heusler compounds,[40] where Mn tends to exhibit a large value of μMn with the nominal electron configuration of Mn3+: [Ar] 3d4 and the oxidation state of 3+.[35]

Figure presents the projected DOS of sub-Mn1 3d and sub-Mn2 3d orbitals (d, d, d, d, d), respectively, in the (LaO)MnAs system for U = 1 eV. We find that all the sub-Mn 3d orbitals are separated at the different energy levels. This result is obtained despite the fact that the HS state significantly dominates the Mn 3d orbital, indicating the absence of the JT effect. We suggest that the separations between sub-Mn 3d orbitals may be induced by the second-order JT effect.[41] This effect may contribute to the LSD in MnAs4 tetrahedra. Furthermore, [LaO]+ and [MnAs]− layers fit each other in the interface between both layers. This mechanism may lead to the LSD in OLa4 tetrahedra, as MnAs4 tetrahedra are distorted. In Figure a, we find that the spin-up valence and conduction d states have the highest peaks at −3.84 and 1.50 eV, respectively, at which these two peaks tend to be localized. This result suggests the exchange splitting of around 5.35 eV. On the other hand, the other sub-Mn1 3d orbitals tend to spread along with the valence and conduction band. Figure c shows that the energy level of −3.84 eV is very close to the lowest DOS valley of As 4p states. Therefore, we roughly suggest that, alongside the localization, the valence d states also show the weakest hybridization with the valence As 4p states. This feature is in contrast to the conduction band, where the highest peak of d states is in the close energy level to that of As 4p states. The result of the Mn2 site is the same as that of the Mn1 site with an opposite spin direction as shown in Figure b. For both Mn1 and Mn2 sites, the Mott-insulating behavior is characterized by the Eg transition between the valence and conduction d/d states.

Figure 7

Projected density of states (DOS) of (a) sub-Mn1 3d and (b) sub-Mn2 3d in the (LaO)MnAs system. The value of U = 1 eV is used.

Conclusions

The structural, electronic, and magnetic properties of the antiferromagnetic (LaO)MnAs system have been comprehensively investigated. The first-principle calculation shows that the increase in U in the Mn 3d orbital induces the increment of the LSD at MnAs4 and OLa4 tetrahedra, where the LSD at OLa4 is more pronounced than that of MnAs4 tetrahedra. Since Mn 3d is half occupied, the LSD at MnAs4 tetrahedra is induced by the possible second-order JT effect. It is also shown that the increase in U induces the increase in Eg, which has the maximum value at U = 8 eV, and μMn. Based on the structural properties, the value of U = 1 eV is the most appropriate value for the system in the present work despite the underestimated Eg of 0.834 eV. This U value also results in a μMn of 4.31 μB, respectively. Furthermore, the lower μMn than the theoretical value for the HS state is promoted by the strong hybridization between Mn 3d and As 4p states. Among all the sub-Mn 3d orbital, we find that the valence d states show the less pronounced hybridization with valence As 4p states. Both valence and conduction d states are localized at −3.84 and 1.50 eV, respectively. Moreover, it is suggested that the Mott-insulating behavior in the system is characterized by the transition between d/d states at the valence band maximum and conduction band minimum. From the projected DOS, the second-order JT is suggested by the separations between all sub-Mn 3d states, where d and d states are at the same energy levels. Finally, this work presents the new insights of the properties of the system, which are essential for future functional device applications.