Key Takeaways & Executive Findings
- •• • High-throughput screening of 1470 binary configurations identified 37 dynamically stable pentagonal monolayers, including 24 previously unreported structures, expanding the design space for 2D materials. • • Room-temperature magnetism is achieved with ferromagnetic Curie temperature up to 521 K, antiferromagnetic Néel temperature up to 761 K, and altermagnetic Néel temperature of 984 K, enabling spintronic devices operating at ambient conditions. • • Altermagnetic semiconductor Mn4N2 exhibits giant spin splitting of 0.78 eV and pure spin-polarized transport window from −0.04 to 0.36 eV, with strain-tunable valley splitting of 18.2 meV under 4% uniaxial strain, offering tunable spin-valley coupling for quantum information processing. • • Type-II multiferroicity in Fe4C2 and Mn4C2 shows in-plane electric polarization of 1.408 and 1.564 pC/m, ferroelastic strain of 0.8% and 1.2%, and reversal chirality, enabling multifunctional devices with coupled ferroic orders.
Abstract
Two-dimensional planar pentagonal crystals, long pursued for their geometrically frustrated lattice configurations and emergent quantum phenomena, have remained challenging to realize due to the intrinsic incompatibility of regular pentagons with Euclidean tiling. Here, we unveil 37 dynamically stable binary planar pentagonal monolayers through high-throughput computational screening of 1470 stoichiometric candidates. These materials exhibit room-temperature magnetism, including ferromagnetic (Curie temperature up to 521 K), antiferromagnetic (Néel temperature up to 761 K), and altermagnetic (Néel temperature = 984 K) ground states, alongside unprecedented electronic states: Dirac semimetals, Dirac half-metal, nodal-loop semimetal, nodal-loop half-metal, and altermagnetic semiconductors (Mn4N2) with giant spin splitting (0.78 eV). The latter achieves pure spin-polarized transport windows (−0.04 to 0.36 eV) and strain-tunable valley splitting (18.2 meV under 4% uniaxial strain). Intrinsic type-II multiferroicity emerges in Fe4C2 and Mn4C2, featuring in-plane electric polarization (1.4 and 1.6 pC/m), ferroelasticity (0.8% and 1.2% reversible strain), and reversal chirality. Topological band analysis identifies chiral edge states in Dirac semimetal pentagons, alongside a magnetic topological insulator with Chern number |C| = 2 in Mo2S4 and W2Te4. Temperature-driven structural transitions in Os2S4 and Tc2S4 from pentagonal to Lieb lattices accompany topological state switching and metal-to-semiconductor transitions. This work establishes pentagonal lattices as a platform for symmetry-driven multifunctionality, bridging geometric frustration with applications in spintronics, nanoelectronics, and quantum devices.
1. Introduction
Two-dimensional (2D) materials have revolutionized condensed matter research since the isolation of graphene, with their electronic properties dictated by structural motifs through well-established structure-property relationships. While high-symmetry hexagonal, triangular, square, and kagome lattices dominate due to their inherent compatibility with Euclidean tessellation, planar pentagonal systems remain exceptionally rare because regular pentagons cannot tile 2D space without gaps. This fundamental geometric constraint, formalized by the isolated pentagon rule, has historically precluded the development of stable 2D pentagonal materials. Mathematically, 2D space can be fully tessellated using irregular pentagons through Cairo-type configurations, where four adjacent pentagons form a stretched hexagonal motif with D2h symmetry. Inspired by this principle, penta-graphene, a planar 2D carbon allotrope composed of distorted pentagons, was proposed, exhibiting a 3.15 eV bandgap and anomalous mechanical properties such as negative Poisson’s ratio. Subsequent theoretical studies have expanded this family to over 100 pentagonal lattices spanning elemental, binary, and ternary compositions, with diverse symmetries (planar to buckled) and stoichiometries (2:1 to 1:5). These materials display remarkable mechanical, electronic, magnetic, thermal, topological, and optical properties, enabling diverse potential applications. Experimental progress has been significant, though challenging. The smallest fullerene C20, composed entirely of pentagons, was synthesized prior to penta-graphene’s prediction. Recent breakthroughs in symmetry-adapted corrugated design and mechanical exfoliation, exemplified by puckered PdSe2 and PdTe2, demonstrate viable pathways to overcome these topological constraints. High-pressure synthesis yields novel phases, but the lack of systematic computational screening has hindered the discovery of stable pentagonal monolayers with desired functionalities.
This study addresses the bottleneck by performing high-throughput density functional theory (DFT) calculations to systematically investigate electronic and magnetic properties in 2D pentagonal lattices. Tight-binding analysis reveals intrinsic metallic states, band gaps, Dirac cones, and nodal loops near the Fermi level. High-throughput first-principles screening of 1470 binary configurations identified 37 dynamically stable systems, including 24 previously unreported structures. These materials exhibit diverse magnetic ground states (FM, AFM, and AM) with room-temperature magnetism, and host rich electronic phases encompassing NM metal, NM semiconductor, FM half-metal, Dirac semimetal, Dirac half-metal, nodal-loop semimetal, nodal-loop half-metal, AF metal, AF semiconductors, and AM semiconductor. Notably, altermagnet Mn4N2 exhibits substantial spin splitting of 0.78 eV and strain-dependent electronic structure transitions, while thermal perturbations induce pentagon-to-Lieb transitions in Os2S4 (600 K) and Tc2S4 (800 K), accompanied by topological/metal-insulator transitions. Topological invariants classify Hg2C4, Os2S4, Fe4N2, Ni4C2, Pd4C2, and Pt4C2 as topological insulators with chiral edge states, while Mo2S4 and W2Te4 exhibit |C| = 2. Fe4C2 and Mn4C2 demonstrate type-II multiferroicity with in-plane polarization (1.408 and 1.564 pC/m), with barriers (0.16 and 0.26 eV/atom), ferroelastic strain (0.8% and 1.2%), and reversal chirality. These results establish pentagonal lattices as a platform for correlated electronic, magnetic, and topological phenomena, informed by symmetry-driven structure-property relationships.
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ZHANG Kai, LI Yifan, WANG Dayong, LV Haifeng, WU Xiaojun (2026). Computational Screening of 2D Pentagonal Materials with Room-Temperature Altermagnetism, Multiferroicity, and Topological States. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3600-1
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Frequently Asked Questions
What is the thermal stability of the predicted pentagonal monolayers, and how do they compare to experimentally realized 2D materials like PdSe2?
The 37 dynamically stable monolayers were confirmed via phonon calculations, indicating they are local minima on the potential energy surface. For instance, Os2S4 and Tc2S4 undergo structural transitions to Lieb lattices at 600 K and 800 K, respectively, suggesting that some pentagonal phases may be metastable at elevated temperatures. In contrast, PdSe2 is experimentally stable up to its decomposition temperature, but the predicted materials offer a broader range of electronic and magnetic properties, making them promising for room-temperature applications.
How robust is the altermagnetic spin splitting in Mn4N2 against strain and temperature, and what are the implications for spintronic devices?
Mn4N2 exhibits a giant spin splitting of 0.78 eV, which is exceptionally large for altermagnets. Under 4% uniaxial strain, the valley splitting reaches 18.2 meV, indicating strong strain tunability. The spin-polarized transport window spans −0.04 to 0.36 eV, which is robust against small perturbations. However, the Néel temperature of 984 K suggests high thermal stability, making it suitable for room-temperature spintronic applications.
What are the practical challenges in synthesizing these predicted pentagonal monolayers, and what experimental routes are suggested?
Synthesis of planar pentagonal lattices is challenging due to the geometric frustration of regular pentagons. However, recent successes with PdSe2 and PdTe2 via mechanical exfoliation from bulk layered materials suggest that similar approaches could be applied if bulk precursors exist. Alternatively, chemical vapor deposition (CVD) on suitable substrates might be feasible, as demonstrated for other 2D materials. The high-throughput screening provides a list of promising candidates, but experimental validation is required.
How do the topological properties of Mo2S4 and W2Te4 (Chern number |C| = 2) compare to known quantum anomalous Hall insulators, and what are the potential applications?
Mo2S4 and W2Te4 are predicted to be magnetic topological insulators with Chern number |C| = 2, which is higher than the typical |C| = 1 in many QAH insulators. This leads to two chiral edge channels, potentially enabling dissipationless spin currents with higher efficiency. The band gap is not explicitly stated, but the topological invariant suggests robust edge states. These materials could be used in low-power electronic devices and quantum computing.
What is the computational methodology used to predict the Curie and Néel temperatures, and how reliable are these estimates compared to experimental values?
The Curie and Néel temperatures were estimated using Monte Carlo simulations based on the Heisenberg model with exchange parameters derived from DFT. This approach typically overestimates T_C and T_N by 10-20% due to neglect of quantum fluctuations and anharmonic effects. However, the relative trends among materials are reliable. For example, the altermagnetic T_N of 984 K in Mn4N2 is exceptionally high, suggesting strong magnetic exchange interactions.
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