Andreas Hermann, Edinburgh

 

I am a Reader in the School of Physics and Astronomy at the University of Edinburgh. My research is in the field of computational materials science: using first-principles, parameter-free computing methods to predict and understand properties of materials - such as their stability, elastic, electronic, and optical attributes.


As member of the Centre for Science at Extreme Conditions, a part of my research focuses on the occurrence of new, interesting phases of various materials under conditions of extreme compression and high temperatures.

About Me

Contact

Office 2604

School of Physics and Astronomy

James Clerk Maxwell Building

Peter Guthrie Tait Road

The University of Edinburgh

Edinburgh, EH9 3FD


Phone +44 131 650 5824

Email a.hermann@ed.ac.uk

Join the group

Students interested to join the group for a PhD are always welcome. Research projects can be found on the School’s web pages, together with information on the application process.


Potential undergraduate research projects are listed on the School’s wiki page (requires login).


News


01/2021: Disintegration of water at planetary pressures

Water is a major component of icy planets’ interiors. In mixtures with other important species, such as methane or ammonia, it can change in unexpected ways. We had previously predicted that water molecules in a water-ammonia mixture would completely disintegrate under pressure, leaving behind an ionic solid instead of a hydrogen-bonded molecular crystal. Now, Raman spectroscopy measurements have detected the fingerprints of this ionic phase in high-pressure experiments. The work, led by Eugene Gregoryanz’ group, has just been published in Phys. Rev. Lett.


01/2021: Cooperative diffusion “pre-melting” in compressed calcium

Melting is not necessarily an all-or-nothing deal. In certain circumstances, a melted state can coexist with a solid state. One such example in high-pressure scenarios we previously studied is “chain melting” where 1D chains of atoms in a crystalline lattice “melt” while the surrounding atoms remain fixed. Now, using simulations based on quantum mechanics and machine learning, we show that even the simplest possible crystal structure can support chain melting, as the simple cubic phase of calcium exhibits a thermally excited regime of cooperative diffusion. The work, led by Jian Sun, is now published in Phys. Rev. X.


11/2020: Thermal excitations in dense weakly interacting matter

Methane is a good approximation of a noble gas element: basically spherical, inert, not forming bonds with other atomic or molecular species. This changes under pressure, and in a study led by Jian Sun and now published in Natl. Sci. Rev., we investigated thermally excited states in dense helium-methane mixtures, revealing a hierarchy of states from the solid to the fluid regime.


10/2020: Rare earth hydride superconductivity

Rare earth polyhydrides under pressure are amongst the best superconductors known. We have now shown, in a study published in Phys. Rev. B, that a ‘second island’ of high-Tc superconductivity exists in the late lanthanide hydrides, with superconducting Tc around 100 K in YbH10 and LuH8.


10/2020: High-energy density materials from molecular mixtures

Polymeric nitrogen is a promising high-energy density material. Pressure is needed to transform nitrogen from a molecular N2 crystal to macromolecular (Nm) or polymeric form. Here, in a computational study led by Feng Peng and published in Phys. Rev. Materials, we show that mixing N2 with methane, CH4, can result in molecular CxNyHz compounds with high energy density at lower pressures than required for pure nitrogen.


10/2020: Structural and electronic transition in topological matter

Tin telluride, SnTe, is a proposed topological crystalline insulator. Real samples are always non-stoichiometric and undergo a phase transition at low temperatures that breaks topological protection of several electronic states. Here, in a study published in Phys. Rev. B and led by experiments by Chris O’Neill and Andrew Huxley, we show the impact of this transition on SnTe’s Fermi surface, and how the transition can be suppressed by pressure.


07/2020: Transition metal hydride

Pressure-induced formation of metal polyhydrides is of interest in new electronic materials. Here, in a study published in J. Phys. Chem. Lett., we supported experimental efforts by Eugene Gregoryanz and Ross Howie to provide detailed properties of a new cobalt hydride, CoH3, stabilised under pressure.


04/2020: Planetary mixtures

Icy planets’ atmospheres contain a large amount of hydrogen and helium. How do these relatively inert species interact with the molecular ices that make up the mantle regions of these planets? Our recent study on helium-ammonia interactions, led by Jian Sun and published in Phys. Rev. X, showed that their interaction is much richter than hitherto thought, with intriguing high-temperature behaviour. See also the synopsis in APS Physics.


02/2020: Realistic materials strength calculations in ceramics

Ultra-high temperature ceramics (UHTC) are promising materials for a wide range of applications in the energy and transport sectors. In recent work led by Weiguo and Cheng Lu, now published in Phys. Chem. Chem. Phys., we performed realistic calculations on mechanical failure of a prototypical UHTC material, TaC, which resulted in very good agreement with experimental hardness results.


01/2020: Plasticity and superionicity in molecular mixtures

Elevated temperatures can induce intriguing states in compressed molecular systems. In our recent study published in J. Phys.:Cond. Mat. we explored mixtures of water and ammonia, which serve as proxies for icy planet mantle regions, across composition, pressure, and temperature, using ab initio molecular dynamics calculations.

This invited paper forms part of the Emerging Leaders 2019 collection of contributions, “bringing together the best early-career researchers from all areas of condensed matter physics”.