Novel ammonia-hydrogen sulphide mixtures under extreme conditions: Implications for Ice-giant planets

Author: Guest blogger
Posted: 12 Feb 2021 | 13:14

Sudip Kumar Mondal from Jadavpur University in Kolkata visited the University of Edinburgh through the HPC-Europa3 Transnational Access programme. Falling from 11 October to 29 January, Sudip's visit was unlike most others because the Covid pandemic was ongoing. In this blog post Sudip describes his experiences in coming to and working in Edinburgh.

My doctoral research focuses on the physical behaviour of naturally occurring mineral phases at high temperature and pressure conditions by employing quantum chemical simulations which are hard to realize through experiments at the laboratory. Dr Andreas Hermann, my supervisor at the University of Edinburgh, was undoubtedly perfect for supervising this project, being an expert on materials at extreme conditions.

What I experienced at Edinburgh is surely a bit distinct from other visits since my entire visit was during the Covid pandemic! But the cooperation and hospitality I received  was so wonderful that I did not feel any different. I arrived in Edinburgh on October 11th and had to self-isolate for two weeks. Thanks to Pancakes, the Persian cat of my host, for making those fourteen days eventful. Catherine Inglis and William Lucas from EPCC were just an email away if I needed anything. William was extremely helpful in setting me up on Cirrus (a Tier-2 national service hosted by EPCC). Catherine was instrumental in processing my academic documents and financial aid. Initially, I got acquainted with my host Dr Hermann on Skype and started submitting jobs even before we met in person.

I was full of excitement when the final day of my self-isolation came to an end and I was able to meet Dr Hermann at the King's Buildings campus. He generously showed me around the campus and took me to the James Clerk Maxwell Building which appeared like a labyrinth! We then got involved in scientific conversations and setting up the workplan and timeline of the visit. The discussion about the advancement from my side continued in the following weeks, together with submitting new jobs to Cirrus, extracting results and more discussions. I am grateful to Dr Hermann for the enriching confabs.

Earlier my research focused only on the mineral phases found in terrestrial planets. This project went beyond it and gave me the opportunity to work on H2S-NH3 molecular crystals proposed by Dr Hermann to form the interior of the gas giant planets Uranus and Neptune. The state of H2S and its interaction with the other chemical species are still doubtful, yet crucial to model those planets’ interiors as H2S and NH3 form deep NH4SH clouds in the lower atmospheres of Uranus and Neptune. This project aimed to determine the partial diffusivity (superionicity) and full melting curve of the relevant molecular crystalline phases by employing ab-initio molecular dynamics (AIMD) simulation as implemented in VASP. H2S itself metallises and becomes superconducting in ultra-high-pressure regimes. Exploring the possibility of potential metallisation and the feasibility of a superconducting phase via electron-phonon coupling calculations also constitutes a material-science inspired target of this project. By running the AIMD simulations on Cirrus at EPCC, Edinburgh, we have found the melting conditions of the ambient low-pressure and high-pressure phase where superionicity is observed in the later. Initially, I used to employ first-principal simulation in the framework of density functional theory (DFT) for my research. At Edinburgh, working with Dr Andreas Hermann, I learned the AIMD which was previously unexplored by me. I am confident that the scientific exposure that I had in this visit is going to be very fruitful for my academic career.

My overall experience at Edinburgh was very pleasant. You can imagine the astonishment of someone coming from a city the population of which is three times that of the whole of Scotland! Hence the social-distancing - cakewalk. The Old Town, the cathedrals, the stone paved streets and the architectural marvels caught me by surprise. Occasional walks in the park like Holyrood or Calton Hill with a latte in one hand was rejuvenating.

Needless to say, there were very few people in public places, buses had only four or five passengers, the central Waverley station was empty, but that was the different world I craved to get acquainted with. As the rules got stricter after Boxing Day the streets became emptier, giving me the perfect opportunity to try my hand at amateur photography. 

Although the sky was overcast most of the time during the visit, I was blessed with the sight of the great Jupiter-Saturn conjunction and, that too from the mesmerising top of Edinburgh Castle. The same planets which we are trying to simulate appeared in the sky to give us a sneak peek: beat that strange sensation! I have encountered snow in the Himalayas but the snowfall in Edinburgh hit different: something every Edinburgher looks forward to.

Although I enjoyed the benefits of digital connectivity, I still feel that in-person meetings and discussions are much more immersive, entertaining and fun. However, remote meetings and discussions over the internet facilitate people from different part of the world to come together to exchange ideas, and are budget friendly! I am not sure about the right balance between these two forms, but both are necessary depending on the circumstances.

In summary, the whole visit was an enjoyable and enriching experience for me. The only regret I have is that I did not get to see the shops and the crowd at Prince's Street Gardens on Christmas Eve which I was told is a must-visit. Hopefully someday in the future I will be able to do that. I left Edinburgh on January 29th, but Edinburgh did not leave me.

Pardon me for not including the customary picture of Edinburgh Castle! Enjoy the sunset at Calton Hill and Saint Giles Cathedral instead.

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