OpenMX developers meeting
Nov. 10th, 2023

Structure search, database, andapplications for AB2 type 2D materials

Institute for Solid State Physics,
University of Tokyo
Masahiro FUKUDA
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Structure search, database, andapplications for AB2 type 2D materials• Structure search for AB2 monolayer– structure map

M. Fukuda, et. al., Mater. Adv., 2, 4392-4413 (2021).

• Database– interactive website– data repository• Applications– memory structure– penta monolayer (η-Au2S, θ-Au2S)
M. Fukuda, et. al., arXiv:2305.08111 [cond-mat.mtrl-sci]
2Structure search for AB2 monolayer• Research purpose– Structure exploration for AB2 type monolayers by high-throughput density
functional theory (DFT) calculations• Background– Various kinds of AB2 type monolayers such as transition metal dichalcogenides(e.g. MoS2) and MXenes (e.g. Ti2C) have synthesized experimentally and haveattracted attentions due to the diversity of the chemical and physical properties.
– The combination of the elements is diverse even only for the AB2 composition.
→ Sufficient room for exploring unknown AB2 monolayers

1T• Approach

1H– High-throughput calculations based on the DFT by using OpenMX[1] wereperformed to create a structure map for AB2 type monolayers.

[1] OpenMX, http://www.openmx-square.org/.

3

Structure search for AB2 monolayer• Research purpose– Structure exploration for AB2 type monolayers by high-throughput density
functional theory (DFT) calculations• Background– Various kinds of AB2 type monolayers such as transition metal dichalcogenides(e.g. MoS2) and MXenes (e.g. Ti2C) have synthesized experimentally and haveattracted attentions due to the diversity of the chemical and physical properties.
– The combination of the elements is diverse even only for the AB2 composition.
→ Sufficient room for exploring unknown AB2 monolayers• Approach– High-throughput calculations based on the DFT by using OpenMX wereperformed to create a structure map for AB2 type monolayers.

4High-throughput calculation based on the DFT• Software: OpenMX(http://www.openmx-square.org/)• Functional: GGA-PBE• Pseudo potential: Optimized Pseudo atomic orbitals• k-point : 5×5×1• Cutoff energy: 240 [Ry]• Variable cell optimization and symmetry-unconstrained
geometry optimization• Selection of composition elements

Possible AB2 compounds: 62 elements×62 elements = 3844 compounds

5Initial structures
1T1HPlanar• We prepared the initial structures including fluctuation with respect to the ideal structures
for atomic coordinates. The initial lattice vectors for variable cell optimizations were set
to large enough to allow large structural change from the initial structure and to avoid
trapping of local minima as far as possible.
• If the structure change drastically from the initial structure, we terminate the calculation.

3844 (compounds) × 3 = 11532

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Structure map
Space-groupclassification

Space-groupclassification

1T

1H

We set an acceptable energy range
0.03 Hartree (≈ 0.82 eV) per the unit
cell for comparison among structures
obtained from three initial states.
This structure map includes information of initial structuresand space-groups of obtained structures for all the combinationof AB2 compounds.

8Comparison between experiment and calculation(transition metal dichalcogenides)
Experimental data by high-resolution STEM imaging[2]

ATi

ZrHfS

1T

1T

1T

Se

1T

BTe

1T(a)
(b)

(c)

1T

(d)

1TVNbTaMo

WReFePdPt(e)

1T

1H

1H

1H

1H

1T′′－－

1T

1T(f)

1T

1H

1H

1H

1H

1T′′

1H－

1T－－

1T－

1T′－－－－(g)

1T′
1H

(h)

[2] J. Zhou et al., Nature 556, 355 (2018)

Results of high-throughput DFT calculations
BA

Ti

Zr

HfV

Nb

TaMo

W

ReFe

PdPtSSe

Te－
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Comparison between experiment and calculation(transition metal dichalcogenides)
Experimental data by high-resolution STEM imaging[2]ATiZr

HfS

1T

1T

1T

Se

1TB

Te

1T(a)
(b)

(c)

1T(d)

1TV

NbTaMoW

ReFePdPt(e)

1T

1H

1H

1H

1H

1T′′－

－

1T

1T

(f)

1T

1H

1H

1H

1H

1T′′

1H－

1T－

－

1T－

1T′－－－－(g)

1T′
1H

(h)

[2] J. Zhou et al., Nature 556, 355 (2018)

1T

1H

1T′

1T′′

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Comparison between experiment and calculation(transition metal dichalcogenides)
Experimental data by high-resolution STEM imaging[2]

A

Ti

Zr

HfS

1T

1T

1T

Se

1TBTe

1T(a)
(b)

(c)

1T(d)

1TVNbTaMoWReFePdPt(e)

1T

1H

1H

1H

1H

1T′′－

－

1T

1T(f)

1T

1H

1H

1H

1H

1T′′

1H－

1T－

－

1T－

1T′－－－－(g)

1T′
1H

(h)

[2] J. Zhou et al., Nature 556, 355 (2018)

Results of high-throughput DFT calculations
B

ATi

Zr

HfV

NbTaMoW

ReFe

PdPtSSe

Te－
11Families of AB2 type 2D materials••••••

1T/1H
B

AIIITMI2II2TM

11 11 22XII18XIII

22XIV

517 20

XV10 10 16

XVI20 13 18

XVII17 14XII

15transition metal dioxides/dichalcogenides → TM-XVItransition metal dihalides → TM-XVII
alkaline-earth-metal dihalides → II-XVII
MXenes (transition metal carbides/nitrides) → XIV-TM, XV-TM
dialkali-metal monochalcogenides, monohalides → XVI-I, XVII-I
dialkaline-earth-metal monochalcogenides, monohalides → XVI-II, XVII-II
XIII XIVXV XVI XVII

235231145819 63 47
121231118947111235831521216

The number of 1T/1H type AB2monolayers for each combination ofgroups in the periodic table aresummarized on the basis of our structuremap.
→This table can be a guide to search
unknown 1T/1H structures and families.

12Structure search, database, andapplications for AB2 type 2D materials• Structure search for AB2 monolayer– structure map

M. Fukuda, et. al., Mater. Adv., 2, 4392-4413 (2021).

• Database– interactive website– data repository• Applications– memory structure– penta monolayer (η-Au2S, θ-Au2S)
arXiv:2305.08111 [cond-mat.mtrl-sci]
13

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Interactive website

The interactive website is linked with
OpenMX viewer(www.openmx-square.org/viewer/).

Our AB2 structure map and database are available on theinteractive website, www.openmx-square.org/2d-ab2/.

15• Data repository using Gitlab• Download all the input files and results easily→ Promoting data utilization

https://datarepo.mdcl.issp.u-tokyo.ac.jp/repo/616Structure search, database, andapplications for AB2 type 2D materials• Structure search for AB2 monolayer– structure map

M. Fukuda, et. al., Mater. Adv., 2, 4392-4413 (2021).

• Database– interactive website– data repository• Applications– memory structure– penta monolayer (η-Au2S, θ-Au2S)
arXiv:2305.08111 [cond-mat.mtrl-sci]
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NEB calculation formemory structure of SrAl2
Energy barrier ~ 2eV
0001

0111

Since the positions (above orbelow) of red atoms can represent
binary digits, we call the buckled
structures “memory structure”.

0011
0000

1111

This structure can be a candidate
for a data storage application withan extremely high areal density.
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Penta-monolayers obtained in structure search
for AB2 type monolayers by high-throughput DFT calculations
planar

Au2B

buckledC2Ge

PbSe2

Experimentally synthesized monolayer
J. Am. Chem. Soc. 2017, 139, 14090−14097

θ-Au2S

η-Au2S

Q. Wu, et. al., The J. Phys. Chem. Lett. 10, 3773 (2019)θ-Au2S(Discovered by
HTP calculations ofAB2 2D materials)

5.67[Å]
Total energy = -443.3368[Hatree/unit cell]= -13.7901 [Hatree/ Å2]

η-Au2S

5.84[Å]
Total energy = -443.3399 [Hatree/unit cell]= -12.9990 [Hatree/ Å2] 21

Analysis of geometric structures and physical properties
of Au2S monolayer under strain based on DFT

Energy (eV / unit cell)

DFT: GGA-PBE
Program code: OpenMX(http://www.openmx-square.org/)

Compressive biaxial strain causes the phase transition
from η-Au2S to θ-Au2S. The band structure and bandgap
of Au2S are changed drastically under strain because of
the phase transition.

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Band decomposition into each contribution of pseudo-atomic orbital
Au-s

Au-dAu-p

η-Au2Sp orbital bandd orbital band23Band decomposition into each contribution of pseudo-atomic orbital
Au-s

Au-p

Au-d

θ-Au2S

Mixing of p and d orbital bands

24θ-Au2Se

η-Au2Se

θ-Au2Teη-Au2Te25

η-Au2S

η-Au2P

η-Au4PSThe mixing of atomic
species changes theFermi level and theband structure.
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Summary•

High-throughput calculations based on DFT by using OpenMX have been
performed to create a structure map for AB2 type monolayers.

•The structure map of AB2 type 2D materials will give new viewpoints anddirections to search unknown 2D materials.

•Our structure map is available in the interactive website and ISSP Data Repository(Gitlab).

•NEB calculation for SrAl2 indicated that it may be possible to control some of
memory structures as binary digits storage applications.

•The band structures and bandgaps of Au2S, Au2Se and Au2Te, are changed
drastically under strain because of the phase transition (θ ↔ η).

•The family of Au2X type monolayer may have a potential to acquire a diversity ofphysical quantities by replacing the X element or absorbing additional atoms
without breaking the basic Au lattice network.
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