Department of Physics and Astronomy

Condensed matter theory

People and contact

Prof. Rajeev AhujaDr. Sudip Chakraborty, Dr. Anton GrigorievDr. C. Moyses AraujoDr. Wei LuoAmitava BanerjeeRafael Barros Neves de AraujoThanayut KaewmarayaVivekanand Shukla, Teeraphat WatcharatharapongJohn Wärnå

Office
Å13106
Telephone
+46 18 471 3626
Email

rajeev.ahuja@physics.uu.se

Research

2D Catalytic-Materials

In particular, we predict the enhanced water splitting activity of recently synthesized two dimensional (2D) semiconducting materials MX2 (where M= Ti, Hf, Zr and X=S, Se, Te), hydrogenated silicene, stanene and phosphorene from the band edge alignment concept. The real catalytic mechanism of water dissociation is hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) which are needed to be envisaged together with the band edge alignment. A fundamental understanding of how to improve solar hydrogen production with such 2D materials is of great technological importance. We have performed a theoretical investigation [12] in order to find the optimum photocatalytic activity of ultra-thin silicane and germanane with a series of functionalizing adatoms. HER and OER activity are determined from the surface-adsorbate interaction. This study can be an intuitive way to theoretically rationalize HER and OER activity for a series of functionalized different two-dimensional systems before performing the actual experiment in the laboratory. A comparative study of HER mechanism on WS2 and PtS2 monolayers has also been performed recently [3]. The lightest 2D catalytic material has been found in the form of Boron monolayer based on our electronic structure calculations [4]. We have also investigated a novel defect engineered g-C3N4 nanosheet produced by hydrogen treatment [5]. On the basis of experimental as well as DFT calculations, it has been shown that the formation of two-coordinated nitrogen vacancy in g-C3N4 is responsible for the narrowed band gap and the enhancement in solar absorption. With improved optical absorption in the visible range, higher surface area, open pore structure, and lower rate of electron−hole recombination of the defective g-C3N4, it leads to higher photocatalytic activity as compared to pristine g-C3N4.

  1. Theoretical Evidences Behind Bifunctional Catalytic Activity in Pristine and Functionalized Al2C monolayer, R Almeida, A Banerjee, S Chakraborty, J Almeida, R Ahuj, ChemPhysChem,(2017)
  2. Rationalizing Hydrogen and Oxygen Evolution Reaction Activity of Two-dimensional Hydrogenated Silicene and Germanene, C. Rupp, Sudip Chakraborty, J. Anversa, R. Baierle, R. Ahuja, ACS Appl. Mater. Interfaces, 8, 1536 (2016).
  3. The effect of impurities in ultra-thin hydrogenated silicene and germanene: A first principles study, C. Rupp, Sudip Chakraborty, R. Ahuja, R. Baierle, PhysChemChemPhys17, 22210 (2015).
  4. A Comparative Study of Hydrogen Evolution Reaction on WS2 and PtS2 pseudo-monolayer: Insight based on Density Functional Theory, S. H. Mir, Sudip Chakraborty, J. Warna, S. Narayan, P. C. Jha, P. K.  Jha, R. Ahuja, Catalysis Science & Technology 7, 687-692 (2017).
  5. Two-dimensional Boron: Lightest Catalyst for Hydrogen and Oxygen Evolution Reaction, S. Mir, Sudip Chakraborty, P. K. Jha, J. Warna, H. Soni, P. Jha, R. Ahuja, Applied Physics Letters, 109, 053903 (2016).
  6. Defect Engineered g-C3N4 for Efficient Visible Light Photocatalytic Hydrogen Production, Q. Tay, P. Kanhere, C. Ng, S. Chen, Sudip Chakraborty, A. Huan, T. Sum, R. Ahuja, and Z. Chen, Chemistry of Materials, 27, 4930 (2015).

Crystal structure prediction from first-principles: random search and metadynamics simulations

The properties of a material are highly dependent on the crystal structure. We develop ab initio theory capable to predict new structures, utilizing the search tools to explore the configurational space based on genetic algorithm methods, random search methods, data mine approaches, topological modeling methods, and metadynamics. We employ this method to study the structure of the novel complex light metal hydrides as well as to investigate the H₂ dissociation on the metal hydride surfaces. Predicting crystal structures is a computational time-consuming task, therefore we spend a lot of time on optimizing the computational methods.

  1. Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries, Rafael B Araujo, Amitava Banerjee, Rajeev Ahuja, J. Phys. Chem. C, 2017, 121 (26), pp 14027–14036

Hydrogen storage

Light-metal hydrides and high-surface area materials are considered as promising hydrogen storage systems. We explore both kinds in terms of their electronic structure with the aim of understanding existing hydrogen desorption mechanisms, and possibly predict ways to improve their functionality.

The understanding of H₂ dissociation on metal surfaces is a key point toward the design of suitable hydrogen storage materials. We calculate the H₂-dissociation energy barriers with the Nudged Elastic Band Method and investigate the effect of impurities on these barriers. We aim on catalysts design that fasten the H-sorption reactions in novel hydrogen storage materials. 

An extensive review on Hydrogen Storage Materials for stationary and mobile applications has been published recently [3]. We have also shown the hydrogen storage enhancement in 2D materials like silicene and its hydrogenated counterpart [4] and hydrogen desorption from MgH2 [5]. 

  1. Nanostructured materials for solid-state hydrogen storage: A review of the achievement of COST Action MP1103.Callini, E., Aguey-Zinsou, K., Ahuja, R., Ramon Ares, J., Bals, S. et al. International journal of hydrogen energy, 41(32): 14404-14428, 2016.
  2. Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art. Lai, Q., Paskevicius, M., Sheppard, D., Buckley, C., Thornton, A. et al. ChemSusChem, 8(17): 2789-2825, 2015.
  3. Hydrogen storage materials for mobile and stationary applications: Current state of the art, Q. Lai, A. Thornton, M. Hill, Z. Haung, H.K. Lui, Z. Guo, M. Paskevicius, D. Sheppard, C. Buckely, A. Banerjee, Sudip Chakraborty, R. Ahuja, K.F. Aguey-Zinsou, ChemSusChem (Review), 8, 2789 (2015).
  4. Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage, T. Hussain, T. Kaewmaraya, Sudip Chakraborty, R. Ahuja, PhysChemChemPhys, 15, 43, 18900 (2013).
  5. Improvement in Hydrogen Desorption from β and γ-MgH2 upon Transition Metal Doping, T. Hussain, T. A. Maark, Sudip Chakraborty, R. Ahuja, ChemPhysChem, 16, 12, 2557 (2015). (Selected Cover Article)

Molecular electronics

Molecular electronics is a rapidly developing research field at the interface of physics, chemistry, and engineering, in which electron transport through molecules is investigated. The project involves design and ab initio simulations of molecular structures, metal and semiconductor surfaces and molecular adsorption applied to molecular electronics, biological- and nano-sensors and synthesis of novel materials. Our research is performed within the environment of the Uppsala University UniMolecular Electronics Center (U³MEC) which focuses on molecular electronics based on single or small assemblies of molecules.

Organic batteries

Organic based battery materials can be produced from biomass and are expected to have a significantly lower environmental footprint from raw material extraction and material processing. Current organic matter based alternatives offer capacities comparable to their inorganic counterparts but in most cases they suffer from poor cycling stability, low conductivity or large polarization losses. In this project the combination of a conductive polymer backbone with high capacity redox groups is studied to overcome capacity fading due to dissolution as well as conductivity pathways through the material.

  1. Assessing the electrochemical properties of polypyridine and polythiophene for prospective applications in sustainable organic batteries. Rafael B Araujo, Amitava Banerjee, Puspamitra Panigrahi, Li Yang, Martin Sjödin, Maria Strømme, C Moyses Araujo, Rajeev Ahuja. Physical Chemistry Chemical Physics 19 (4), 3307-3314
  2. Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application. Rafael B Araujo, Amitava Banerjee, Puspamitra Panigrahi, Li Yang, Maria Strømme, Martin Sjödin, Carlos Moyses Araujo, Rajeev Ahuja.  J. Mater. Chem. A, 2017, 5, 4430-4454

Solar cell

The Organic-Inorganic hybrid perovskites have opened new avenues to develop low cost and high efficiency photovoltaic devices. Perovskites with general formula MAX3 (M=Organic part; A=Pb, Sn; X= Halogens) have attracted significant attention as efficient light harvesters. In particular, CH3NH3PbI3 has been intensely studied over past couple years for solar cell applications. Solar cells based on the hybrid perovskites have shown efficiencies more than 20%, claiming these materials as potential candidates for next generation solar devices. Lead based perovskite solar cells are relatively new devices and modeling of these materials is focused on understanding the materials properties. Additionally, searching Lead free hybrid perovskite is another interesting future challenge of this field. We also focus on stability of Guanidium (GA) based hybrid perovskites GAPbI3 and GAPbBr3 hybrid perovskite along with electronic properties and solar energy conversion efficiency. Further alloying of GAPbI3 will be considered to evaluate formation probability of intermediate alloy. The outcome is planned to be connected with the experimental observations to have a more impact in the scientific community.

  1. Bromination Induced Stability Enhancement with Multivalley Optical Response Signature in Guanidinium [C(NH2)3]+ Based Hybrid Perovskite Solar Cells, Amitava Banerjee, Sudip Chakraborty, Rajeev Ahuja, Journal of Materials Chemistry A 5(35):18561-18568 (2017)
  2. Substitution induced band structure shape tuning in hybrid perovskites (CH3NH3Pb1-xSnxI3) for efficient solar cell applications, P. Kanhere, Sudip Chakraborty, C. Rupp, R. Ahuja, Z. Chen, RSC Advances, 5, 107497 (2015)
  3. Rational Design and Combinatorial Screening Approach for Lead free and Emergent Hybrid Perovskites, Sudip Chakraborty, W. Xie, N. Mathews, M. Sherburne, R. Ahuja, Mark Asta, S. G. Mhaisalkar, ACS Energy Letters 2, 837 (2017)

Solar fuel production (Photoelectrocatalysis)

A promising sustainable solution for solar energy harvesting and utilization is artificial photosynthesis: the sunlight is used to split the water molecules and subsequently reduce the CO₂, producing methane and methanol. We computationally design photoelectrocatalysts suitable for such application.

Topological insulators

Topological insulators attract increasing attention due to the novel quantum state based on quantum spin Hall effect and hence the potential applications in quantum computation and spintronics. We are extensively working on the the pressure-induced topological insulating behavior in experimentally synthesized materials based on first principles electronic structure calculations. Ge2Sb2Te5 is one such interesting materials where we have found topological insulating behavior under the external pressure and strain. [1, 2] GeTe/Sb2Te3 phase-change superlattice is another interesting material that shows topological insulating behavior. [3] Recently, we have demonstrated how the superconducting critical temperature can be tuned with the external high pressure in Sb2Se3 [4] and Sb2Te3 [5] topological insulators.

  1. Pressure-induced topological insulating behavior in the ternary chalcogenide Ge2Sb2Te5, B Sa, J Zhou, Z Song, Z Sun, R Ahuja, Physical Review B 84, 085130 (2011)
  2. Strain-induced topological insulating behavior in ternary chalcogenide Ge2Sb2Te5. B Sa, J Zhou, Z Sun, R Ahuja, Europhysics Letters, 97, 27003 (2012)
  3. Topological insulating in GeTe/Sb2Te3 phase-change superlattice B Sa, J Zhou, Z Sun, J Tominaga, R Ahuja, Physical review letters 109 (9), 096802, 2012.
  4. High pressure driven superconducting critical temperature tuning in Sb2Se3 topological insulator, J Anversa, Sudip Chakraborty, P Piquini, R Ahuja, Applied Physics Letters 108, 212601 (2016)
  5. Superconductivity in Topological Insulator Sb2Te3 Induced by Pressure, J. Zhu et al. Scientific Reports 3, 2016 (2013)

Full list of publications

Publications up to April 2015.

Selected Publications