🎙Chengcheng Xiao,
Nicholas Bristowe and Arash Mostofi
Origin story
- Q: Can we freezing electrons off-atom?
- A: Hum.. We'll probably need:
- Electron donating elements
- A way to stabilize them
Molecular crystal of Cs⁺(18-crown-6)₂e⁻
Ref: James L. Dye et al., Synthesis of cesium 18-crown-6: the first single-crystal electride?, J. Am. Chem. Soc. 1982, 104, 13, 3781–3782
Crown ethers
Cs
Prof. James L. Dye
(1927-2021)
Origin story
- But we don't like organic stuff, inorganic crystals? Pretty please? 🥺
Mayenite-Ca₁₂Al₁₄O₃₃
Ref: W. Buessem and A. Eitel,Z. Kristallogr., Kristallgeom.,Kristallphys., Kristallchem., 1936,95, 175–188.
Ref: Hideo Hosono, et al. ,High-Density Electron Anions in a Nanoporous Single Crystal: [Ca24Al28O64]4+(4e-),Science, 2003,301,626–629.
- Mayenite have a framework of pores occupied by O²⁻ ions
- Once we coaxed them out as oxygen, we are left with electrons @ site.
Calcium
Oxygen
Aluminum
Origin story
more?
Yttrium
- Interstitial sites lie in a 2D plane between Yttrium atoms.
Y₂C
Ref: Zhang Xiao, et.al. Chem.Mater.2014, 26, 6638−6643
Carbon___
Okay, can we have
2D electron gas like behavior
Origin story
Strontium
Bismuth
Sr₅Bi₃
- Interstitial sites lie in a 1D cavity surrounded by strontium atoms.
Ref: Lee A. Burton, et.al. Chem.Mater.2018, 30, 7521−7526
More! !
Origin story
- Interstitial sites lie in a 0D cavity surrounded by Sodium atoms.
Na-hp4
Ref: Yanming Ma, et.al. Nature, 2009, 182-185, 458(7235)
More! ! !
High pressure (~200Gpa)
Elemental system
Origin story
- Electron emitters: R. H. Huang and J. L. Dye,Chem. Phys. Lett., 1990,166,133–136
- Superconductors: Zenner S. Pereira, et al. J. Phys. Chem. C 2021, 125, 8899-8906
- Battery anodes: J. Hu, et al ,ACS Appl. Mater. Interfaces, 2015,7, 24016–24022
- Catalysts: Michikazu Hara, et al. ACS Catal. 2017, 7, 4, 2313–2324
Applications (properties):
Ref: Xiaoha Z., Recent Advances and Applications of Inorganic Electrides, J.Phys. Chem. Lett. 2020, 11, 3841-3852
Ref: Hideo Hosono, Advances in Materials and Applications of Inorganic Electrides, Chem. Rev. 2021, 121, 3121-3185
Definition
"Ionic" compounds in which electrons are localized at interstitial sites and act as anions.
- Electride materials is that they are:
Sodium - hp4
GoalS
- Understand the underlying mechanism that links all types of electrides together*.
- Based on the theory, find a descriptor to identify electrides from databases.
*no unifying theory has been proposed, to the best of our knowledge.
- Theory + descriptor + high-throughput calculations
- The connections to different areas
Electrides are materials with (electron-deficient, distance-optimized) multicentered bonding formed by orbitals of surrounding atoms*.
*Simlar idea were also proposed by Xiao Dong and Artem R. Oganov, (2017), Electrides and Their High-Pressure Chemistry, In G. G. N. Angilella, Antonino La Magna (editors) Correlations in Condensed Matter under Extreme Conditions, Springer Press, and by M. Hanfland et al. ,New high-pressure phases of lithium, Nature, (2000), 174-178, 408.
Theory
strain
Resonance-like
Metallic-like
Descriptor-ELF
-
Electron localization function (ELF): tells the degree of localization of electrons based on Pauli exclusion principle.
- ELF is a scalar field just like charge density
- ELF = 0 → delocalized; ELF = 1 → localized
Ref: Andreas Savin, et al., ELF: The Electron Localization Function, Angew. Chem. Int. Ed. Engl., 1997,36,1808-1832
Ref: A. D. Becke and K.E. Edgecombe, A simple measure of electron localization in atomic and molecular systems, J. Chem. Phys., 1990, 92, 5397.
To identify the multicentered bonding:
Charge density maxima @ interstitial site
ELF maxima @ interstitial site
ELF-isosurface
Known 2D electride: Y₂C
- ELF gives the location of the multicentered orbital.
- But how do translate this interpertation into an automated process?
Ref: Huaqing Huang, et al., Topological Electride Y₂C, Nano Lett., 2018, 18(3), 1972-1977
DESCRIPTOR-ELF
Topological analysis: Bader partition the space based on ELF zero-flux planes.
sites with more than 2 atoms (of the same type) surrounding it → potential electride site.
ELF maxima
Atoms
DESCRIPTOR-ELF
Criteria for systems to be identified as electride:
High value ELF maxima @ center of atomic cage.
High ELF Bader basin integrated charge number.
Basic requirement.
There are enough charge occupying this state.
ResultS
High-throughput screening of electrides:
- A total of ~55000 entries on the Materials Project data base is sampled.
- Around 10000 entries were found to possess interstitial ELF maxima (regardless of value).
ResultS
ResultS
Our prediction for more electride-like systems
metallic-bonding systems
ResultS
Metallic bonding also have this feature and the transition to electride-like bonding is smooth!
Our prediction for more electride-like systems
metallic-bonding systems
ResultS
Metallic bonding also have this feature and the transition to electride-like bonding is smooth!
Our prediction for more electride-like systems
metallic-bonding systems
Ref: Zhu Q., et al., Computational Discovery of Inorganic Electrides from an Automated Screening,Matter, 2019, 1293-1303, 1(5).
ResultS
Metallic bonding also have this feature and the transition to electride-like bonding is smooth!
Our prediction for more electride-like systems
metallic-bonding systems
Ref: Zhu Q., et al., Computational Discovery of Inorganic Electrides from an Automated Screening,Matter, 2019, 1293-1303, 1(5).
http://chengcheng-xiao.github.io/electride-db/
ResultS
ResultS
- That leads to 629 (mostly new) electrides:
- 428 non-magnetic materials
- 201 magnetic materials
- As an starting point, we suggest checking systems with:
- ELF maxima value > 0.8
- Occupation (per spin channel) > 1.0
COnnections
How does our theory and results can be used to understand:
- Metallic systems vs electeides
- Origin of properties
- Organic electrides
S-orbitals
# of entries
Previously predicted electrides*
Ref: Zhu Q., et al., Computational Discovery of Inorganic Electrides from an Automated Screening,Matter, 2019, 1293-1303, 1(5).
S-orbitals
- The s-orbitals of alkaline and alkaline earth metals are very dispersive + have no direction dependency.
Na
K
- How come we don't see many group I and II elemental systems being identified as electrides?
S-orbitals
- Q: How come we don't see any group I and II elemental systems being identified as electrides?
- A: Most elemental group I and II systems don't meet the distance criteria and the multicentere bonds are "weak".
edge cases
- But in some edge cases, we do have electride-like elemental metal systems!
Should they be identified as electrides?
ELF max:0.7
Occ.: 1.51
ELF max: 0.7
Occ.: 1.92
Intermetallics
- The question ‘‘Are Intermetallic Phases Electrides?’’ wasalready posed decades ago*.
* R. Nesper,Angew. Chem., Int. Ed. Engl., 1991,30, 789–817
Intermetallics
- The question ‘‘Are Intermetallic Phases Electrides?’’ wasalready posed decades ago*.
* R. Nesper,Angew. Chem., Int. Ed. Engl., 1991,30, 789–817
Intermetallics
- Intermetallic systems can have way more atomic arrangements comparing to elemental systems.
- At the same time, because metallic-like bonding is not easy to differentiate from electride-like bonding.
- The question ‘‘Are Intermetallic Phases Electrides?’’ wasalready posed decades ago*.
* R. Nesper,Angew. Chem., Int. Ed. Engl., 1991,30, 789–817
Our answer:
d-orbitals?
- d-orbital electrides do exist!
- They exist in smaller cages than s-orbital electrides
- They are less likely to have high polarizability but other features.
FM
AFM
2D-LaBr
⭐️Unifying theory
- Inorganic electrides (atomic orbital)
- High pressured electrides (atomic orbitals)
- Organic electrides
⭐️Unifying theory
Inorganic electrides (atomic orbital)High pressured electrides (atomic orbitals)- Organic electrides
HOMO
LUMO-1
LUMO-2
LUMO-3
- The HOMO and LUMOs act like atomic orbitals.
- HOMO is s-shaped.
More stories can be found on the origin of these orbitals. In our view they should be categorized as SAMOs (Super Atomic Molecular Orbitals). But other argue they are metal atoms' extended s-orbitals.
Na-Tripip222
Organic ones
Point Defects
Bounce round: F-center defects (atomic orbtial)
Ref: Ferenc Karsai, et al.,F-center in lithium fluoride revisited: Comparison of solid-state physicsand quantum-chemistry approaches, Phys. Rev. B, 2019, 89(12).
Ref: Janotti, Anderson, Hydrogen multicentre bonds, science, Nature Materials, (2007), 44-47, 6(1)
- Li:[He] 2s1
- F:[He] 2s2 2p5
- Li +: [He]
- F−:[He] 2s2 2p6
1 electron @ defect site
Electride: periodic arrangement of point defects?
Take-aways
Electride are systems with (electron-deficient, distance-optimized) multicenterd bonds.
We have constructed a composite descriptor that can quantitatively tell the likelihood of a system being an electride.
Future plan
- Detailed analysis of specific cases using more sophisticated methods like Natural Bond Orbitals (NBO), Solid State Adaptive Natural Density Partitioning (SSAdNDP) and Crystal Orbital Bond Index (COBI). Detailed blog posts of these method, coming soon!
- Focus on three cases:
- A system that is most electride-like.
- A prototypically metallic system (for comparison)
- A system that is previously identified electride but not with our method.
Future plan
- Finish several old projects
- LaBr flat band, alpha T3 model
- Multiferroicity of LaBr hydride (La2HBr2)
- Analysis of (inter)metallic systems that behave "almost" like electride and bond analysis of Mg for Binxing
thank yOu 🤟
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MAKING ELECTRIDES
We need two criterias to be satisfied:
- Occupation criteria
- Distance criteria
Doping!
Strain!
MAKING ELECTRIDES
BCC-Sodium
We can force a system with metallic bonding into an electide by tensile strain.
ELF max: 0.5505
Occ.: 0.1604
MAKING ELECTRIDES
Tetragonal-Sodium
We can force a system with metallic bonding into an electide by tensile strain.
ELF max: 0.7266
Occ.: 0.7470
Making electrides
This time, we use doping to bring out electride nature inside an typical ionic material
NaCl-Doped [4e]
ELF max: 0.7525
Occ.: 0.4094
Results
# of entries
Systems with Charge maxima points
COBI [Ca₆Ge₂O]
COBI [Ca₆Ge₂O]
