Studies of the Earth's atmosphere have shown that more than 90% of the expected amount of Xe is depleted, a finding often referred to as the ‘missing Xe paradox’. Although several models for a Xe reservoir have been proposed, whether the missing Xe could be contained in the Earth's inner core has not yet been answered. The key to addressing this issue lies in the reactivity of Xe with Fe/Ni, the main constituents of the Earth's core.

CALYPSO predicted a chemical reaction of Xe with Fe/Ni at the temperatures and pressures found in the Earth's core. It find that, under these conditions, Xe and Fe/Ni can form intermetallic compounds, of which XeFe3 and XeNi3 are energetically the most stable. This shows that the Earth's inner core is a natural reservoir for Xe storage and provides a solution to the missing Xe paradox. (see Li Zhu et al., Nature Chem. 6.644 (2014))

While apply CALYPSO surface reconstruction prediction method on a simple diamond (100) surface, an unexpected surface reconstruction featuring self-assembled carbon nanotubes arrays arises. Such a surface is energetically competitive with the known dimer structure under normal conditions, but it becomes more favourable under a small compressive strain or at high temperatures. The intriguing covalent bonding between neighbouring tubes creates a unique feature of carrier kinetics (that is, one dimensionality of hole states, while two dimensionality of electron states) that could lead to novel design of superior electronics. The discovery of the hitherto expected surface structure highlights the power of CALYPSO. (see Shaohua Lu et al., Nature Commun. 5, 3666 (2014))

CALYPSO predicted the structure of stable Cs-F compounds containing neutral or ionic molecules.Their geometry and bonding resemble that of isoelectronic XeFn molecules, showing a caesium atom that behaves chemically like a p-block element under these conditions. The calculated stability of the CsFn compounds shows that the inner-shell electrons can become the main components of chemical bonds. (see Mao-sheng Miao, Nature Chem. 5, 846 (2013))

CALYPSO predicted the thermodynamically structures and a large number of metastable phases of tungsten borides. These results clarify and correct previous structural assignments and predict new structures for possible synthesis. The findings provide crucial insights for understanding the rich and complex crystal structures of tungsten borides, which have broad implications for further exploration of this class of promising materials. (see Li et al., Phys. Rev. Lett. 110, 136403 (2013))

The structural evolution of solid carbon dioxide (CO2) under high pressure was studied by using CALYPSO. The results show that, although it undertakes many structural transitions under pressure, CO2 is quite resistive to structures with C beyond 4-fold coordination. It has been a longstanding and challenging objective to stabilize C in a hypervalent state, particularly when it is bonded with nonmetallic elements. Most of the work so far has focused on synthesizing organic molecules with a high coordination number of C. This results provide a good measure of the resistivity of C toward forming hypervalent compounds with nonmetallic elements and of the barrier of reaction involving C−O bonds. (see et al., J. Am. Chem. Soc. 135, 14167 (2013))

Superconductive sodalite-like CaH6 was predicted by CALYPSO method at high pressure.The structure of CaH6 proved to be remarkably stable and led to the types of electron-phonon interactions known to produce superconductivity in other materials. The temperature of transition (known as the critical temperature) was between 220 and 235 K, much higher than any known superconductor, and within reach of high-end refrigeration systems. (see Wang et al., Proc. Natl. Acad. Sci. USA 109, 6463 (2012))

The pressure-induced formation of a hydrogen symmetric atomic phase (I-42d structure) and a partially ionic phase (monoclinic P21 structure) consisting of coupled alternate layers of (OH)δ- and (H3O)δ+ (δ=0.62) in water ice was predicted by CALYPSO method. The occurrence of this ionic phase follows the break-up of the typical O-H covalently bonded tetrahedrons in the hydrogen symmetric atomic phases and is originated from the volume reduction favourable for a denser structure packing.(See Wang et al., Nature Commun. 2, 563 (2011))

CALYPSO predicted the dissociation of molecular oxygen into a polymeric spiral chain O4 structure (space group I41/acd, θ-O4) above 1.92-TPa pressure. Stabilization of θ-O4 turns oxygen from a superconductor into an insulator by opening a wide band gap (approximately 5.9 eV) that originates from the sp3-like hybridized orbitals of oxygen and the localization of valence electrons. (see Zhu et al., Proc. Natl. Acad. Sci. USA 109, 751 (2012))

A novel carbon allotrope of C-centered orthorhombic C8 ( Cco-C8 ) is predicted by using CALYPSO method on structural search. Cco-C8 adopts a sp3 three-dimensional bonding network that can be viewed as interconnected (2, 2) carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs over a wide range of pressures studied (0-100 GPa).(see Zhao et al., Phys. Rev. Lett. 107, 215502 (2011))

CALYPSO predicts new stable structures of 2D boron-carbon (B-C) compounds for a wide range of boron concentrations. (see Luo et al., J. Am. Chem. Soc. 133, 16285 (2011))

Eight fascinating sp2- and sp3- hybridized carbon allotropes have been uncovered using CALYPSO method. These crystalline allotropes can be viewed respectively as three-dimensional (3D) polymers of (4,0), (5,0), (7,0), (8,0), (9,0), (3,3), (4,4), and (6,6) carbon nanotubes, termed 3D-(n, 0) or 3D-(n, n) carbons. (see Zhao et al., ACS Nano 5, 7226 (2011))

CALYPSO predicts the most energetically favorable insulating structure of lithium reported so far (see Lv et al., Phys. Rev. Lett.106, 015503 (2011)). The predicted ABA2-40 (Pearson's symbol: oC40) structure has been confirmed by Guillaume et al.'s experiments. (see Guillaume et al. Nature Phys. 7, 211 (2011))

CALYPSO has been applied to the determination of long-puzzled high pressure structures of Bi2Te3, which remain unsolve since 1972. Above 14.4 GPa, we experimentally discovered that Bi2Te3 unexpectedly develops into a Bi-Te substitutional alloy by adopting a body-centered cubic disordered structure stable at least up to 52.1 GPa. (see Zhu et al., Phys. Rev. Lett. 106, 145501 (2011))