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All-t_{2g} Electronic Orbital Reconstruction of Monoclinic MoO_{2} Battery Material

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## Abstract

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## Featured Application

**The dielectric function and optical conductivity are used to evaluate voltage-capacity profiles, as their shape is rooted in the multi-orbital nature of the redox process in battery materials. This represents a firm approach to characterise materials for energy storage, and battery materials in particular, and offers a robust predictive framework for novel battery materials, one that can be rapidly matched to measurable quantities.**

## Abstract

## 1. Introduction

## 2. Results and Discussion

#### 2.1. Correlated Electronic Structure

#### 2.2. Optical Conductivity

#### 2.3. Voltage-Capacity Using LDA+DMFT

## 3. Materials and Methods

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Partial LDA densities-of-states (DOS) of MoO${}_{2}$ within the monoclinic symmetry. Notice the splitting of LDA the bands into bonding and antibonding branches in the projected ${d}_{{x}^{2}-{y}^{2}}$ DOS, a characteristic property of monoclinic materials.

**Figure 2.**Crystal structure of MoO${}_{2}$ of monoclinic symmetry (Mo blue, O red), atomic coordinates and cell parameters are taken from Ref. [36]. Short Mo-Mo contacts are represented as blue sticks. The monoclinic unit cell is highlighted in green. The distorted octahedral coordination of Mo by O is represented as transparent polyhedron. A 3 × 2 × 3 supercell was chosen.

**Figure 3.**Effect of electronic correlations on the orbital-resolved LDA+DMFT density-of-states (DOS) of monoclinic MO${}_{2}$. Worth noticing is the dynamical evolution of the ${d}_{{x}^{2}-{y}^{2}}$ bonding-antibonding branch, which shows an overall shift to energies above ${E}_{F}$ due to correlation-induced spectral weight transfer. Also relevant is the formation of a pseudogap-like state at energies near the Fermi level (${E}_{F}=\omega =0.0$) for $U=5$ eV.

**Figure 4.**Bottom panel: Role of electron–electron interactions on the total LDA+DMFT DOS. LDA results are shown for comparison. Notice the formation of a lower Hubbard band at energies close to −2 eV and the evolution of the reconstructed electronic structure above ${E}_{F}$. The top panel shows the theory-experiment comparison between LDA+DMFT one-particle spectral functions and the photoemission spectra taken from Ref. [19]. Notice the good theory-experiment agreement at low energies and the correlation induced transfer of spectral weight compared to LDA from low to high binding energies.

**Figure 5.**Orbital resolved optical conductivity of monoclinic MoO${}_{2}$ computed within LDA+DMFT. Notice the changes in the Drude-like peak below $0.5$ eV and its evolution with increasing U. For the ${x}^{2}-{y}^{2}$ orbital also relevant is the energy position of the first optical conductivity peak at 0.72 eV for $U=4.5$ eV which is in semi-qualitative agreement with experimental data taken from Ref. [22]. As discussed in the text, the two main peaks in optics are fingerprints of particle-hole excitations within the correlated monoclinic phase of MoO${}_{2}$.

**Figure 6.**Rate capability of stoichiometric MoO${}_{2}$ within LDA+DMFT in the potential (V) window relevant for future battery applications. Experimental voltage-capacity profiles of MoO${}_{2}$ taken from Refs. [27] (triangles) and [16] (diamond) are shown for comparison. (The experimental data was shifted upward to coincide with theory at low specific capacities.) Notice the good qualitative agreement between the experimental data and the LDA+DMFT results for $U=3.5$ eV.

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**MDPI and ACS Style**

Craco, L.; Leoni, S.
All-*t*_{2g} Electronic Orbital Reconstruction of Monoclinic MoO_{2} Battery Material. *Appl. Sci.* **2020**, *10*, 5730.
https://doi.org/10.3390/app10175730

**AMA Style**

Craco L, Leoni S.
All-*t*_{2g} Electronic Orbital Reconstruction of Monoclinic MoO_{2} Battery Material. *Applied Sciences*. 2020; 10(17):5730.
https://doi.org/10.3390/app10175730

**Chicago/Turabian Style**

Craco, Luis, and Stefano Leoni.
2020. "All-*t*_{2g} Electronic Orbital Reconstruction of Monoclinic MoO_{2} Battery Material" *Applied Sciences* 10, no. 17: 5730.
https://doi.org/10.3390/app10175730