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Crystals
Special Issues
Computational and Theoretical Insights into Superconductors Advancements
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Computational and Theoretical Insights into Superconductors Advancements

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: 16 August 2024 | Viewed by 1868

Special Issue Editors

Dr. Xiaoyu Wang

E-Mail Website
Guest Editor
Department of Chemistry, University at Buffalo, Buffalo, NY 14260, USA
Interests: strong correlation matter; electron–phonon interaction; crystal structure prediction; superconductivity; quantum physics and chemistry
Dr. Francesco Belli

E-Mail Website
Guest Editor
Department of Chemistry, University at Buffalo, Buffalo, NY 14260, USA
Interests: electron–phonon interaction ; anharmonicity; quantum nuclear effects; machine learning; superconductivity; hydrides
Prof. Dr. Eva Zurek

E-Mail Website
Guest Editor
Department of Chemistry, University at Buffalo, Buffalo, NY 14260, USA
Interests: first principles calculations; electronic structure, density functional theory; crystal structure prediction; high pressure chemistry; superconductivity; superhard materials; catalysis; self-assembly; low-dimensional systems

Special Issue Information

Dear Colleagues,

The phenomenon of superconductivity has the yet-untapped potential to revolutionize advancements in medicine, energy storage, transportation, and quantum computing. The well-understood mechanism of conventional BCS superconductivity has paved the way for theoretical predictions, computational methods, data science, and artificial intelligence (AI) to play a crucial role in advancing the field. Concurrently, the experimental confirmation of higher-temperature superconductivity has marked a transformative moment in the field, stimulating further theoretical studies. Advanced computational methods, including crystal structure prediction, have become powerful tools for efficient material design, enabling the exploration of different crystal structures and compositions. Additionally, the development of novel theoretical infrastructure has enhanced the speed and accuracy of predicting superconducting critical temperatures. Such methods facilitate the exploration of a broader range of chemical components, the investigation of quantum anharmonic effects, and the analysis of structural engineering factors such as strain–stress relationships and low-dimensional materials, thereby enabling the prediction of potential superconductors with desirable properties, empowering the discovery of novel materials. The present Special Issue on "Computational and Theoretical Insights into Superconductor Advancements" serves as a comprehensive report summarizing the tools and theories that currently define the field, and the recent progress that has been made therein, encouraging further studies in this area.

Dr. Xiaoyu Wang
Dr. Francesco Belli
Prof. Dr. Eva Zurek
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • superconductor
  • electron–phonon interaction
  • crystal structure prediction
  • quantum anharmonic effect
  • superconductivity
  • machine learning
  • material discovery

Published Papers (2 papers)

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Research

21 pages, 5316 KiB  
Article
Superlattice Symmetries Reveal Electronic Topological Transition in CaC6 with Pressure
by Bruce Wang, Antonio Bianconi, Ian D. R. Mackinnon and Jose A. Alarco
Crystals 2024, 14(6), 554; https://doi.org/10.3390/cryst14060554 - 14 Jun 2024
Viewed by 784
Abstract
The electronic properties of calcium-intercalated graphite (CaC6) as a function of pressure are revisited using density functional theory (DFT). The electronic band structures of CaC6, like many other layered superconducting materials, display cosine-shaped bands at or near the Fermi [...] Read more.
The electronic properties of calcium-intercalated graphite (CaC6) as a function of pressure are revisited using density functional theory (DFT). The electronic band structures of CaC6, like many other layered superconducting materials, display cosine-shaped bands at or near the Fermi level (FL). Such bands encompass bonding/antibonding information with a strong connection to superconducting properties. Using a hexagonal cell representation for CaC6, the construction of a double supercell in the c-direction effects six-folding in the reciprocal space of the full cosine function, explicitly revealing the bonding/antibonding relationship divide at the cosine midpoint. Similarly, folding of the Fermi surface (FS) reveals physical phenomena relevant to electronic topological transitions (ETTs) with the application of pressure. The ETT is characterised by a transition of open FS loops to closed loops as a function of pressure. As the highest transition temperature is reached with pressure, the dominant continuous, open FS loops shift to a different region of the FS. For CaC6, the peak value for the superconducting transition temperature, Tc, occurs at about 7.5 GPa, near the observed pressure of the calculated ETT. At this pressure, the radius of the nearly spherical Ca 4s-orbital FS coincides with three times the distance from the Γ centre point to the Brillouin zone (BZ) boundary of the 2c supercell. In addition, the ETT coincides with the alignment of the nonbonding (inflection) point of the cosine band with the FL. At other calculated pressure conditions, the Ca 4s-orbital FS undergoes topological changes that correspond and can be correlated with experimentally determined changes in Tc. The ETT is a key mechanism that circumscribes the known significant drop in Tc for CaC6 as a function of increasing pressure. Consistent calculated responses of the ETT to pressure match experimental measurements and validate the examination of superlattices as important criteria for understanding mechanisms driving superconductivity. Full article
(This article belongs to the Special Issue Computational and Theoretical Insights into Superconductors Advancements)
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17 pages, 4079 KiB  
Article
Superlattice Delineated Fermi Surface Nesting and Electron-Phonon Coupling in CaC6
by Bruce Wang, Antonio Bianconi, Ian D. R. Mackinnon and Jose A. Alarco
Crystals 2024, 14(6), 499; https://doi.org/10.3390/cryst14060499 - 24 May 2024
Cited by 1 | Viewed by 854
Abstract
The superconductivity of CaC6 as a function of pressure and Ca isotopic composition was revisited using DFT calculations on a 2c–double hexagonal superlattice. The introduction of superlattices was motivated by previous synchrotron absorption and Raman spectroscopy results on other superconductors that [...] Read more.
The superconductivity of CaC6 as a function of pressure and Ca isotopic composition was revisited using DFT calculations on a 2c–double hexagonal superlattice. The introduction of superlattices was motivated by previous synchrotron absorption and Raman spectroscopy results on other superconductors that showed evidence of superlattice vibrations at low (THz) frequencies. For CaC6, superlattices have previously been invoked to explain the ARPES data. A superlattice along the hexagonal c-axis direction is also illustrative of atomic orbital symmetry and periodicity, including bonding and antibonding s-orbital character implied by cosine-modulated electronic bands. Inspection of the cosine band revealed that the cosine function has a small (meV) energy difference between the bonding and antibonding regions, relative to a midpoint non-bonding energy. Fermi surface nesting was apparent in an appropriately folded Fermi surface using a superlattice construct. Nesting relationships identified phonon vectors for the conservation of energy and for phase coherency between coupled electrons at opposite sides of the Fermi surface. A detailed analysis of this Fermi surface nesting provided accurate estimates of the superconducting gaps for CaC6 with the change in applied pressure. The recognition of superlattices within a rhombohedral or hexagonal representation provides consistent mechanistic insight on superconductivity and electron−phonon coupling in CaC6. Full article
(This article belongs to the Special Issue Computational and Theoretical Insights into Superconductors Advancements)
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