School of Natural Sciences
Seminar by Prof. Katarzyna Pernal, Institute of Physics, Lodz University of Technology, Poland, on September 27, 2021 at 4.00 pm (via Zoom)
Title :
Dynamic Electron Correlation with Adiabatic Connection Approaches: describing excited states and molecular interactions
Abstract :
Correlation energy, despite being a small fraction of the total electronic energy, governs binding of atoms into molecules. Similarly, noncovalent molecular interactions are flawed if the correlation of electrons belonging to interacting subsystems is not accounted for. The two main approaches to electron-correlation involve either perturbation theory or are based on density functionals. They are deficient either in accuracy or computational efficiency and a generally applicable, computationally efficient approach remains a challenge.
Recently we have proposed a novel approach to describing electron correlation in multireference systems by adopting the adiabatic connection (AC) formalism [1]. The latter naturally links electron correlation with fluctuation of density at different points in space. Consequently, the final expression for the correlation energy employs density linear response. In our formalism, we use extended random phase approximation (ERPA) to describe the latter. The proposed AC-ERPA method yields excellent results for ground and excited states of molecules described with the CASSCF wavefunction [2-4]. In my talk I will present applications of the AC methods, and their extensions to multiconfigurational DFT [5], to challenging multireference systems and noncovalently bounded excited state systems.
References
1. K. Pernal, Phys. Rev. Lett. 120 (2018), 013001.
2. E. Pastorczak, K. Pernal, J. Chem. Theory Comput. 14 (2018), 3493.
3. E. Pastorczak, K. Pernal, J. Phys. Chem. Lett. 9 (2018), 5534.
4. E. Pastorczak, M. Hapka, L. Veis, and K. Pernal, J. Phys. Chem. Lett. 10 (2019), 4668.
5. M. Hapka, E. Pastorczak, A. Krzeminska, and K. Pernal, J. Chem. Phys. 152 (2020), 094102
Seminar by Mr. Dinesh Kumar Yadav, Dept. of Chemical Sciences, TIFR, Mumbai on September 16, 2021 at 4.00 pm (via Zoom)
Title:
Protein Electrochemistry: Metal Complexes as a Promoters of the Electron Transfer from a Gold Electrode to Cytochrome c
Abstract:
Direct protein electrochemistry is an important method to determine the redox potential and electron transfer kinetics of metalloproteins. The bare metal electrode generally causes irreversible adsorption and denaturation of the protein on the electrode surface. There have been extensive studies on modification of the gold electrode using thiol functionalized promoters. We have investigated the effect of metal ion binding to a thiol-based Schiff base complex immobilized on the gold electrode for the electron transfer to cytochrome c. Selfassembled Monolayer (SAM) contains Schiff-Base ligand formed by cysteine and salicylaldehyde on the gold electrode was shown to promote quasi-reversible electrochemistry of cytochrome c. Various transition metal complexes of the Schiff-base ligand immobilized on the gold electrode were also found to promote electrochemistry of cytochrome c. The redox potential of the protein was determined to be 0.05±0.02 V (vs Ag/AgCl), which agrees with the reported value. In heterogeneous electron transfer rates for were determined by analyses of the cyclic voltammetric data using Laviron’s equation. The heterogenous electron rate constant (ks) calculated by Laviron’s equation suggest that there is small increase in the electron transfer rates when metal ion (Cr, Fe, Mn) is coordinated to the Schiff base on the electrode surface, suggesting that metal ion coordination possibly stabilizes the SAM of the Schiff base and favours electron transfer to cytochrome c.
Seminar by Dr. Ahin Roy, Trinity College Dublin, Ireland on September 6, 2021 at 4.00 pm (via Zoom)
Title :
Atomic and Electronic Structure of Ultrathin Single-crystalline Nanowires from Electron Microscopy and Simulations
Abstract :
Being the eye of nanomaterials space with atomic-scale resolution, aberration-corrected (scanning) transmission electron microscopy (AC-(S)TEM) can provide a wealth of structural information in low-dimensional materials. With a judicious choice of system of interest, atomistic simulations can facilitate such microscopy. In this talk, I will discuss a couple of such simulation-aided microscopy experiments for different inorganic nanowires.
The talk will focus on structural aspect of symmetry-broken single-crystalline ultrathin Au nanowires, wherein simulations predict that the {111} atomic planes of Au undergo wrinkling, leading to formation of saddle surfaces. Detailed AC-TEM on such wires confirms this prediction. Crystallographic arguments pinpoint the nature of surface stress to be the driving factor behind such structural transformation. Recent AC-STEM experiments with similar scale Pt nanowires show that with a priori crystallographic information, it is possible to reconstruct a 3-D structure from a single projection image of the material, paving a way for suitable alternative to conventional electron tomography. Lastly, in terms of electronic properties, I will briefly talk about Te nanowires, wherein simple adsorption of NO2 shows a semiconductor to metal transition- predicted in simulations and verified by experiments.
Seminar by Dr. Ahin Roy, Trinity College Dublin, Ireland on September 8, 2021 at 2.30 pm (via Zoom)
Title :
Structure-property Correlation in Oxide Materials through Aberration-corrected Electron Microscopy
Abstract :
The unprecedented control of the electron beam in the modern electron microscopes allows diffraction from nanometer regions, and conjunctionally being equipped with spectrometers, they can explore chemical information of the material – establishing much coveted structure-property correlations on-the-go. This can be of great interest to a materials chemist, and I will illustrate a couple of examples in that direction from recent works on oxides.
Firstly, the talk will focus on WO3, which exists in a plethora of crystallographic phases. With judicious choice of chemistry, hexagonal and orthorhombic phases can be selectively accessed. Detailed conventional TEM coupled with simulations lead to insights on the operative growth mechanism in that process. Moreover, an epitaxial phase transformation, viz. hexagonal to monoclinic has been observed recently, hitherto unknown in literature. This leads to a possibility of phase-selective ion-intercalation in this material, which will be discussed. Such structural changes have pronounced effect on the electrochromic property of the material. In the next part, I will briefly focus on hexagonal perovskite BaMnO3, wherein reduced Mn-states have been observed on the surface and was established as the reason for its catalytic activity.
Seminar by Dr. Sumit Kumar, Institute of Basic Science CSLM, South Korea on August 31, 2021 at 4.00 pm (via Zoom)
Title :
Nano-brick: Designing Nanomaterials for Living system
Abstract :
Nanomaterials have been widely explored in the biomedical field, and it is crucial to choose the right material and engineer it appropriately to achieve the desired properties. A variety of natural and synthetic polymers have been investigated in the field, and they can be engineered for different formulations. Here, I will mainly present how biomolecules can be used to engineer the different forms for surface texturing, self-assembling nanoparticles, and creating a confined nanoenvironment. To be effective in medicine, I will introduce new methods for creating diversity in nanostructures to enable seamless integration with living tissue, where the understanding of nanoscale is necessary. These advanced nanomaterials could enable an effective, minimally invasive, personalized healthcare system. Thorough understanding of underlying mechanisms, and advancing to a robust biomedical solution for healthcare, cellular energy generation, and nanobio-manufacturing, could be further translated into commercial products and therapies. These sophisticated nanobio-hybrid platforms with advanced synthetic routes have potential applications in early disease detection and targeted therapy.