Computational materials theory research group

Atoms, electrons, symmetry, geometry

⊕Sinisa Coh, sinisa.coh@ucr.edu
Associate Professor
University of California, Riverside We are a computational materials research group at the University of California, Riverside working on nanostructured materials, complex oxides, layered materials, magnetic materials, topological insulators, superconductors, and optical properties of real materials. We design, discover, and characterize functional materials using state of the art computational techniques, symmetry, nearsightedness principles, geometry, and topology.

Join us

If you would like to join computational materials theory research group, send an email to sinisa.coh@ucr.edu. Please contact Sinisa Coh if you are either currently a graduate or undergraduate student at UCR, or are planning to join UCR in the near future in either materials science, mechanical engineering, or physics.

Contact information

Email: sinisa.coh@ucr.edu
Office: Bourns Hall room A323
Phone: (951) 827-3375

Research publications

⊕We find that in the mesoscopic regime modification of the material's surface can induce an extensive change of the material's magnetic moment. In other words, perturbation of order N² atoms on the surface of a 3-dimensional solid can change the magnetic moment proportionally to N³.
54. Phys. Rev. B 109, 174431 (2024)

We formulate the spin contribution to the inverse Faraday effect of nonmagnetic metals. We deal with the role of the inversion symmetry, which forces all electronic bands to be at least twice degenerate at every point in the Brillouin zone.
50. Phys. Rev. B 107, 214432 (2023)

We find that in BaTiO3 the phonon angular momentum is dominantly pointing in directions perpendicular to the electrical polarization. Therefore, external electric field in ferroelectric BaTiO3 does not control only the direction of electrical polarization, but also the direction of phonon angular momentum.
45. Phys. Rev. Materials 6, 104410 (2022)

We computed the thermoreflectance spectra of Au from first principles. Our calculations confirm that phonon temperature dominates thermoreflectance of Au. Most of thermoreflectance is due to the effect of the phonon population on electron lifetime.
42. Phys. Rev. Materials 5, 106001 (2021)

We find unusually large cross-polarized Raman signature of Ag phonon mode in CrI3, in agreement with experiments. The signal is present only when the following three effects are considered in concert: ferromagnetism on Cr atoms, spin-orbit interaction, and resonant effects. Somewhat surprisingly, we find that the relevant spin-orbit interaction potential originates from iodine atoms (see above), despite magnetism being mostly on chromium atoms.
41. Phys. Rev. Materials 5, 025202 (2021)

We show that when TiO2 anatase (001) is exposed to hydrogen plasma that the pristine surface (black line) termination becomes unfavorable to another, slightly modified, surface (red line). On this modified surface the topmost TiO2 layer is intact but out of registry with the bottom layers. Nevertheless, the modified surface has significantly improved ability to split water under exposure to sunlight. We show by explicit calculation (see above) of the water splitting reaction that the energy barrier that exists on a pristine surface is not present on the modified surface (blue circle above).
39. Phys. Rev. Materials 4, 075801 (2020)

We report simple expressions that capture the interplay of e-e and e-p interactions on electron distribution relaxation times. We observe a dependence of the dynamics on e-e and e-p interaction strengths that is universal to most metals and is also counterintuitive. While only e-p interactions reduce the total energy stored by excited electrons, the time for energy to leave the electronic subsystem also depends on e-e interaction strengths because e-e interactions increase the number of electrons emitting phonons.
38. Commun. Phys. 3, 179 (2020)

We extract a variable X from electron orbitals Psi_nk and energies E_nk in the parent high-symmetry structure of a wide range of complex oxides. Even though calculation was done only in the parent structure, with no distortions, we show that X dictates material's true ground-state structure.
33. Phys. Rev. Materials 2, 053606 (2018)

We propose an alternative structure of TiO2 anatase that has a higher energy oxygen p-like valence band maximum than pristine TiO2 anatase and thus has a much better alignment with the water splitting levels. This alternative structure is unique when considering a large subspace of possible structural distortions of TiO2 anatase.
31. Phys. Rev. B 95, 085422 (2017)

We show that an optimized projection functions method can automatically construct maximally localized Wannier functions even for bands with nontrivial topology. The resulting Wannier functions contain large imaginary components and are more extended than those in the topologically trivial phase.
29. Phys. Rev. B 94, 125151 (2016)

Motivated by the high superconducting transition temperature of monolayer FeSe on SrTiO3, we propose a potential three-dimensional high-temperature superconductor superlattice FeSe-SrTiO3 and study its structural stability and electronic structure.
27. Phys. Rev. B 93, 245138 (2016)

It is shown that a generic form of an antiferromagnetic wave function opens strong electron-phonon coupling channels in the iron-based superconductors. In the nonmagnetic state these channels exist locally on a single iron atom but are canceled out between the two iron atoms in the primitive unit cell.
24. Phys. Rev. B 94, 104505 (2016)

We show that electron-phonon coupling can induce strong electron pairing in an FeSe monolayer on a SrTiO3 substrate.
19. New J. Phys. 17 (2015) 073027

We have performed a systematic representation-theory-based search for the simplest structures allowing isotropic magnetoelectric coupling. We found 44 such structures, all sharing a common pattern of atomic displacements in the direction of atomic magnetic moments.
16. Phys. Rev. B 88, 121106(R) (2013)

We study topologically nontrivial electronic structure of topological fullerenes or other closed-cage molecules.
15. Phys. Rev. B 88, 155127 (2013)

We find particularly strong modifications to the Raman signal of graphene on platinum, compared to that of suspended graphene. The modifications strongly depend on the relative orientation of the graphene and platinum lattices.
14. Phys. Rev. B 88, 235431 (2013)

We study theoretically the Raman spectrum of the rotated (twisted) double-layer graphene, consisting of two graphene layers rotated with respect to each other by an arbitrary angle theta.
11. Phys. Rev. B 88, 165431 (2013)

Under the application of electrical currents, metal nanocrystals inside carbon nanotubes can be bodily transported. We examine how an iron nanocrystal can pass through a constriction in the carbon nanotube with a smaller cross-sectional area than the nanocrystal itself.
10. Phys. Rev. Lett. 110, 185901 (2013)

Using first-principles density functional theory calculations, we discover an anomalously large biaxial strain-induced octahedral rotation axis reorientation in orthorhombic perovskites with tendency towards rhombohedral symmetry.
6. Phys. Rev. Lett. 106, 235502 (2011)

We present a Wannier-based method to calculate the Chern-Simons orbital magnetoelectric coupling in the framework of first-principles density-functional theory. We anticipate that the Chern-Simons contribution to the magnetoelectric coupling could, in special cases, be as large or larger than the total magnetoelectric coupling in known magnetoelectrics, such as Cr2O3.
5. Phys. Rev. B 83, 085108 (2011)

We extend the Berry-phase concept of polarization to insulators having a nonzero value of the Chern invariant.
2. Phys. Rev. Lett. 102, 107603 (2009)

Among the phases of SiO2 are alpha and beta cristobalites, which have a long and somewhat controversial history of proposed structural assignments and phase-transition mechanisms. We use first-principles calculations to investigate the energy, structure, and local stability of P4_12_12 and I-42d structures.
1. Phys. Rev. B 78, 054117 (2008)

55. Kevin Moseni, Richard B. Wilson, Sinisa Coh
"Electron-phonon coupling in ferromagnetic Fe-Co alloys from first principles"
Submitted to Phys. Rev. Materials.

[PDF] [arXiv]

54. Kevin Moseni, Sinisa Coh
"Orbital magnetization of a metal is not a bulk property in the mesoscopic regime"
Phys. Rev. B 109, 174431 (2024).

[PDF] [journal] [arXiv] [supplement code] [supplement pdf]

53. Mohammed Alghamdi, Palani R. Jothi, Wei-Cheng Liao, Sinisa Coh, Xianqing Lin, Boniface P.T. Fokwa, Jing Shi
"Layer-dependence study of two-dimensional ferromagnets: Fe3GeTe2 and Fe5Ge2Te2"
Appl. Phys. Lett. 124, 192404 (2024).

[PDF] [journal]

52. Ming Lei, Sinisa Coh
"Terahertz magneto-optical response in ferromagnetic Fe-Co-Al alloys"
J. Phys.: Condens. Matter 36 315504 (2024).

Computational materials theory research group

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Research publications

Ph.D. Thesis