Publications

In recent years, the Variational Quantum Eigensolver (VQE) has emerged as one of the most popular algorithms for solving the electronic structure problem on near-term quantum computers. The utility of VQE is often hindered by the limitations of current quantum hardware, including short qubit coherence times and low gate fidelities. These limitations become particularly pronounced when VQE is used along with deep quantum circuits, such as those required by the "Unitary Coupled Cluster Singles and Doubles" (UCCSD) ansatz, often resulting in significant errors. To address these issues, we propose a low-depth ansatz based on parallelized Givens rotations, which can recover substantial correlation energy while drastically reducing circuit depth and two-qubit gate counts for an arbitrary active space (AS). Also, considering the current hardware architectures with low qubit counts, we introduce a systematic way to select molecular orbitals to define active spaces (ASs) that retain significant electron correlation. We validate our approach by computing bond dissociation profiles of water and strongly correlated systems, such as molecular nitrogen and oxygen, across various ASs. Noiseless simulations using the new ansatz yield ground-state energies comparable to those from the UCCSD ansatz while reducing circuit depth by 50–70%. Moreover, in noisy simulations, our approach achieves energy error rates an order of magnitude lower than that of UCCSD. Considering the efficiency and practical usage of our ansatz, we hope that it becomes a potential choice for performing quantum chemistry calculations on near-term

Simulating quantum systems with high accuracy remains one of the fundamental challenges in science, with applications ranging from drug discovery to materials design. In particular, quantum chemical simulations play a pivotal role in advancing fields such as chemistry, materials science, and biology. While classical computational methods have achieved considerable success, their ability to simulate complex quantum systems often requires several approximations, making the results inaccurate. Quantum computers are anticipated to overcome these challenges by providing more accurate simulations of complex quantum systems. However, the current generation of quantum devices is limited by noise and decoherence, restricting their practical applications. To overcome these limitations, hybrid quantum-classical algorithms such as the Variational Quantum Eigensolver (VQE) have been developed. In this review, we discuss several notable examples where VQE and its variants have been successfully applied to quantum chemistry problems, highlighting both the current capabilities and the future potential of quantum computing for quantum chemical applications.

Plasmonic metal nanoclusters (NCs) are widely explored in photocatalysis due to their ability to generate excess energy carriers or hot carriers (HCs) that can transfer to nearby molecules and drive otherwise challenging chemical reactions. In this study, we investigate the efficiency of HC transfer from silver (Ag) NCs of varying sizes to two perfluoroalkyl substances (PFAS), namely, perfluorooctanoic acid and perfluorooctanesulfonic acid. Using real-time time-dependent density functional theory, we present the real-time dynamics of plasmon formation, HC generation, and HC transfer from Ag NCs to PFAS. Our findings reveal that although the probability of direct hot electron transfer (DHET) decreases with increasing NC size, the net amount of electron transfer does not exhibit a simple size-dependent trend. Instead, it is governed by the interplay between the electronic structures of the NC and the PFAS molecule. Specifically, smaller NCs exhibit Rabi-type oscillations in charge transfer, indicating back-and-forth electron transfer between Ag nanoclusters and PFAS molecules. In contrast, larger NCs support more unidirectional and stable electron transfer. These findings offer mechanistic insights into size- and electronic structure-dependent HC generation and transfer to PFAS, and provide design principles for more efficient plasmon-driven degradation strategies of PFAS and other related environmental contaminants.

Per- and polyfluoroalkyl substances (PFAS) are widely used in industry and consumer products due to their unique physical and chemical properties. However, due to their toxicity and environmental persistence, the production of long-chain PFAS such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) has been systematically phased out. Instead, short-chain PFAS have been widely used as replacements for long-chain PFAS. However, recent studies indicate that even short-chain PFAS can be toxic to the environment. Despite numerous attempts, complete degradation of these short-chain PFAS has not yet been achieved, leaving room for further exploration. In this work, we explored the potential of plasmonic silver (Ag) and gold (Au) nanoclusters (NCs) in the complete degradation of short-chain PFAS. By considering icosahedral Ag55 and Au55 NCs, as well as different types of PFAS, we present a thorough study of plasmon-induced processes for NC-PFAS complexes. Among different decay channels, our study focuses on plasmon decay through the direct hot electron transfer (DHET) and direct hot hole transfer (DHHT) pathways from NC to PFAS. Our calculations reveal that DHET is more probable in Ag-PFAS complexes and DHHT is more probable in Au-PFAS complexes. Furthermore, among all complexes, the Ag-PFBS complex exhibits the highest DHET with a total probability of 10%. Our Ehrenfest molecular dynamics simulations show that the PFAS in Ag-PFAS complexes undergo efficient degradation in the presence of these hot carriers, albeit at different rates. 

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have recently improved from 10% to ≈20% with non-fullerene acceptors (NFAs) like “Y6.” To further enhance PCEs for commercial viability, modifications are explored to Y6 by replacing pyrrole units with phospholes, leveraging their lower-lying lowest unoccupied molecular orbitals (LUMOs) for better electron-accepting ability. Additionally, terminal fluorine atoms are replaced with electron-withdrawing groups (EWGs) such as Cl, CF3, and NO2, and substituted thiophene units with selenophenes. Using density functional theory (DFT) and time-dependent functional theory (TDDFT), 13 NFAs are studied, evaluating their optoelectronic properties, including short-circuit current density (JSC), open-circuit voltage (VOC), and absorption spectra. Modifications led to red-shifted absorption, improved JSC, and relatively stable VOC values. The PM6/Y6-P-Cl system exhibits the highest PCE of 18.46%. This study highlights the potential for further improving Y6-based OSCs, advancing solar energy efficiency (SDG 7), and contributing to clean energy solutions (SDG 13).

Per- and polyfluoroalkyl substances (PFAS) are a group of forever synthetic chemicals. They are widely utilized in industries and household appliances because of their remarkable stability and distinctive oil- and water-repellent properties. Despite their broad applications, unfortunately, PFAS are hazardous to all forms of life, including humans. In recent years, the environmental persistence of PFAS has raised significant interest in degrading these substances. However, the strong C–F bonds in these chemicals pose several challenges to their degradation. Plasmons of noble metal nanoparticles (NPs) offer many exciting applications, including photocatalytic reactions. However, an atomistic understanding of plasmon-driven processes remains elusive. In this work, using the real-time time-dependent density functional theory, we have studied the real-time formation of plasmons, hot-carrier generation, and subsequent direct hot-carrier transfer from metal NPs to the PFAS. Our simulations show that there is an apparent direct hot-electron transfer from NPs to PFAS. Moreover, using Ehrenfest dynamics simulations, we demonstrated that the transferred hot electrons can efficiently degrade PFAS without requiring any external thermal bath. Thus, our work provides an atomistic picture of plasmon-induced direct hot-carrier transfer from NPs to PFAS and the efficient degradation of PFAS. We strongly believe that this work generates the impetus to utilize plasmonic NPs to mitigate PFAS.

The solid electrolyte interphase (SEI) plays a crucial role in the reversible metal-ion deposition at electrodes, impacting battery performance and lifespan. SEI formation results from the decomposition of salts and solvents at the electrode surface via redox reactions, with its growth governed by dynamic interactions between the electrode, electrolyte, and decomposed products. These interactions are difficult to capture experimentally. Here, using large-scale ab initio molecular dynamics simulations, we explored the formation and evolution of SEIs at the calcium anode under varying solvent, salt, and temperature conditions over 100 ps. Our simulations are inspired by several recent experiments, which show reversible calcium-ion deposition only with a few selected salts under specific experimental conditions. Our work not only deciphers these experiments but also provides detailed microscopic insights into (i) the solvent decomposition, (ii) the order of salt/solvent decomposition in the cell, (iii) the impact of electrode passivation on salt’s stability, and (iv) the role of nuclear dynamics and coordination geometry in anion decomposition, thereby influencing the reversible deposition of cations. These findings offer critical insights into the formation and evolution of SEIs at metal anodes and provide guidance for designing electrolytes to enhance the performance and longevity of metal anode batteries.

Graphene nanoribbons (GNRs) with low band gap and strong near-infrared (NIR) absorption are potential candidates for optoelectronic and biomedical applications. In this context, imide-based GNRs are promising, but there are no rational design principles that yield these robust GNRs with strong NIR absorption. Here, we demonstrate a rational synthesis route to achieve NIR-absorbing imide-based robust GNRs by exploring the bay region of polyperylene (PP). Using the oxidative Diels–Alder reaction, we have successfully introduced mono and diimide functional groups on PP. After cyclodehydrogenation, the resultant GNRs, benzoperylene imide GNR (BPI-GNR) and coronene diimide GNR (CDI-GNR), show oscillatory edge geometry with strong NIR absorption (up to 1000 nm) and optical band gap of ~1.3 eV. Computational studies also indicate that imide substituents play an important role in fine-tuning the optoelectronic properties of GNRs. Moreover, these GNRs are solution-processable and can be made into thin films via spray coating. Owing to the strong NIR absorption and imide substitutions, BPI and CDI-GNRs show good photothermal conversion with excellent cyclic stability.

Three new low-dimensional quaternary sulfides, namely, Tl2Cu2GeS4(1), Tl2Ag2GeS4(2), and Tl2Ag2SnS4(3) were synthesized by solid-state reactions and characterized by single-crystal X-ray diffraction, spectroscopic, thermal, and photocatalytic studies. The compounds 1, 2, and 3, respectively, have centrosymmetric layered, noncentrosymmetric layered, and noncentrosymmetric one-dimensional structures, in which Cu+, Ge4+, and Sn4+ ions have tetrahedral coordination and Ag+ ion has linear, trigonal planar and tetrahedral coordinations. The monovalent thallium cations have TlS8 dodecahedral coordination and TlS7 and TlS6 coordination polyhedra of irregular shape. The compounds 1, 2, and 3 are semiconductors with the respective energy band gap values of 1.68, 2.02, and 1.90 eV. Compared to compounds 1 and 2, compound 3 has a higher efficiency value of 22.9% for the photodegradation of aqueous solution of methylene blue. Band structures and projected density of states of all three compounds were computed using density functional theory, and these results are in good agreement with experiments.

As the lightest 2D material, monolayer borophene exhibits a specific charge capacity of 1860 mA h g−1 for Li-ion batteries, which is four times higher than that of graphite and is one of the highest specific charge capacities ever reported for 2D anode materials. Additionally, it showed high mechanical strength and a low diffusion barrier. However, monolayer borophene suffers from stability issues in its free-standing form, which restricts its real-life applications. Inspired by the recent experimental investigations, which proved the higher stability of bilayer borophene polymorphs (BBPs) over their monolayer counterparts, in this work, we investigated the dynamical and thermodynamical stabilities of both AA– and AB–stacked BBPs in their β12 phase using first-principles calculations. Between the two stacking patterns, we found that only the AB–stacked β12–BBP is both energetically and dynamically stable, and we further investigated its potential as a high-performance anode material for alkali metal-ion batteries. Our investigations show that AB–stacked β12–BBP exhibits good electrical conductivity before and after metal atom (Li/Na/K) adsorption onto it. Further, AB–stacked β12–BBP adsorbs the metal atoms strongly with adsorption energies ranging between −0.89 to −1.44 eV, indicating that there is a lesser possibility of forming dendrites on this anode. Similarly, it has a low diffusion energy barrier (~ 0.13–0.49 eV) for metal atoms, meeting the fast charge/discharge rate requirements. Moreover, it exhibits a reasonably low average metal-insertion voltage (0.43 to 0.65 V) and a specific charge capacity of 330–413 mA h g−1 that is comparable to graphite. All the above findings suggest that the AB–stacked bilayer β12– borophene can be a potentially favorable anode material.

Sodium-ion batteries are considered as potential alternatives to conventional lithium-ion batteries. To realize their large-scale practical applications, it is essential to identify suitable anode candidates exhibiting promising electrochemical properties such as high specific capacity, low diffusion energy barrier, and excellent cyclic stability. In this work, using density functional theory (DFT) calculations and ab initio molecular dynamics simulations, we examine α-graphyne – a carbon-based 2D material – as a potential anode candidate. Our results show that AGY exhibits an ultra-low diffusion barrier of 0.23 eV along both the horizontal and vertical directions and a low average anodic voltage of 0.36 V. Our AIMD studies at 300 K show excellent thermodynamical stability with the loading of four sodium atoms, resulting in a theoretical specific capacity (TSC) of 279 mA h g−1. Doping studies show that varying the nature of acetylenic links of AGY with electron-rich (nitrogen) or electron-deficient (boron) elements, the adsorption strength and diffusion barriers for Na atoms on AGY can be tuned. Furthermore, treating AGY as a case study, we find that conventional DFT studies are expected to overestimate the TSC by a huge margin. Specific to AGY, this overestimation can be up to ∼300%. We identify that ignoring the probable formation of temperature-driven metal clusters is the main reason behind such overestimations. Furthermore, we develop a scheme to calculate TSC with higher accuracy. The scheme, which can be easily generalized to the universal class of electrodes, is evolved by concurrently employing AIMD simulations, DFT calculations and cluster analysis.

Bismuth-based halideperovskite-inspired materials (PIMs) are gaining increasing attention as sustainable and stable alternatives to lead halide perovskites. However, many PIMs have wide band gaps (≥2 eV) and low electronic dimensionality, limiting their utility in optoelectronic applications. In this study, we introduce Cs2AgBi2I9, a two-dimensional perovskite-inspired absorber achieved through partial substitution of Cs+ with Ag+ at the A-site of Cs3Bi2I9. Single-crystal X-ray diffraction analysis reveals that silver atoms occupy the edge sites in the hexagonal lattice, resulting in contracted lattice parameters compared to the parent Cs3Bi2I9. The double A-cation substitution promotes orbital overlap between Ag 5s and I 6p orbitals, leading to a narrower band gap of 1.72 eV and a delocalized electronic structure in Cs2AgBi2I9. Consequently, the 2D-PIM exhibits a three-orders-of-magnitude lower electrical resistivity and an exceptional carrier mobility-lifetime product (μτ) of 3.4 × 10–3 cm2 V–1, representing the highest among solution-processed Bi-PIMs. Furthermore, low-temperature photoluminescence measurements indicate weak electron–phonon coupling, while transient absorption spectroscopy reveals extended hot-carrier lifetimes, suggesting efficient exciton transport in Cs2AgBi2I9. Utilizing these exceptional charge transport properties, Cs2AgBi2I9 photodetectors show a remarkable broad spectral response. This work demonstrates the potential of a double A-site cation engineering strategy to develop low-toxicity PIMs with precisely tailored structural and optoelectronic properties.

This work demonstrates that antigalvanic reactions (AGRs) between thiol-protected plasmonic gold nanoparticles (NPs) and atomically precise silver nanoclusters (NCs) are an interfacial chemistry-driven phenomenon. We reacted 2,4-dimethylbenzenethiol (DMBT)-protected Au NPs (average diameter of 4.46 ± 0.64 nm) with atomically precise [Ag25(DMBT)18]− NC and obtained bimetallic AgAu@DMBT alloy NPs. Systematic investigations with optical absorption spectroscopy, high-resolution transmission/scanning transmission electron microscopy, and elemental mapping revealed the reaction-induced morphological and compositional transformation in NPs. Furthermore, we show that such AGRs get restricted when geometrically rigid interfaces are used. For this, we used 1,3-benzenedithiol (BDT)-protected Au@BDT NPs and [Ag29(BDT)12(TPP)4]3– NCs (TPP = triphenylphosphine). Electrospray ionization mass spectrometric (ESI MS) studies revealed that the interparticle reaction proceeds via metal–ligand and/or metal exchange, depending on the interface. Density functional theory (DFT) calculations and molecular docking simulations were used to understand the interactions and reaction energetics leading to favorable events. Interfacial chemistry of this kind might offer a one-pot synthetic strategy to create ultrafine bimetallic NP-based hybrid materials with potential optoelectronic and catalytic applications.

The cooperative mechanism is of paramount importance in the synthesis of supramolecular polymers with desired characteristics, including molecular mass, polydispersity, and morphology. It is primarily driven by the presence of intermolecular interactions, which encompass strong hydrogen bonding, metal-ligand interactions, and dipole-dipole interactions. In this study, we utilize density functional theory and energy decomposition analysis to investigate the cooperative behavior of perylene diimide (PDI) oligomers with alkyl chains at their imide positions, which lack the previously mentioned interactions. Our systematic examination reveals that dispersion interactions originating from the alkyl side-chain substituents play an important role in promoting cooperativity within these PDIs. This influence becomes even more pronounced for alkyl chain lengths beyond hexyl groups. The energy decomposition analysis reveals that the delicate balance between dispersion energy and Pauli repulsion energy is the key driver of cooperative behavior in PDIs. Additionally, we have developed a mathematical model capable of predicting the saturated binding energies for PDI oligomers of varying sizes and alkyl chain lengths. Overall, our findings emphasize the previously undervalued significance of dispersion forces in cooperative supramolecular polymerization, enhancing our overall understanding of the cooperative mechanism.

Achieving dispersions of antimony sulfide (Sb2S3) in environmentally friendly solvents is of paramount importance for safer and sustainable processing due to its wide range of applications. The efficacy of liquid-phase exfoliation (LPE) depends on the choice of solvents, and the determination of the Hansen solubility parameters (HSP) is crucial. In this work, employing the Hansen solubility sphere method, the HSP values of Sb2S3 are determined to be 20.8, 10.8, and 13.4 MPa1/2, which correspond to dispersive, polar, and hydrogen-bonding interactions, respectively. Environmentally friendly solvents, such as 2-butanol and isopropyl alcohol (IPA), have been identified as good solvents for exfoliation. Subsequently, the stability of the dispersions is investigated using an analytical centrifuge. Through the in situ visualization of transmission profiles and various stability parameters like the instability index, sedimentation velocity, and decay time constants, 2-butanol is found to have excellent dispersion stability. To further explain the observed stability, density functional theory (DFT) calculations are carried out. The adsorption energy of 2-butanol on the surface of Sb2S3 is higher than that of IPA, leading to better solute–solvent interactions and, hence, better dispersion stability. Subsequently, the dispersions are utilized to fabricate thin films using the spray-coating method. The solution-processed Sb2S3 photodetector exhibits an impressive responsivity of 68 mA/W, noise-equivalent power (NEP) of 0.3 pW/Hz–1/2, and detectivity of 2.4 × 1011 Jones.

We present a catalyst-free route for the reduction of carbon dioxide integrated with the formation of a carbon-carbon bond at the air/water interface of negatively charged aqueous microdroplets, at ambient temperature. The reactions proceed through carbanion generation at the α-carbon of a ketone followed by nucleophilic addition to CO2. Online mass spectrometry reveals that the product is an α-ketoacid. Several factors, such as the concentration of the reagents, pressure of CO2 gas, and distance traveled by the droplets, control the kinetics of the reaction. Theoretical calculations suggest that water in the microdroplets facilitates this unusual chemistry. Furthermore, such a microdroplet strategy has been extended to seven different ketones. This work demonstrates a green pathway for the reduction of CO2 to useful carboxylated organic products.

We conducted a thorough evaluation of various state-of-the-art strategies to prepare the ground state wavefunction of a system on a quantum computer, specifically within the framework of variational quantum eigensolver (VQE). Despite the advantages of VQE and its variants, the current quantum computational chemistry calculations often provide inaccurate results for larger molecules, mainly due to the polynomial growth in the depth of quantum circuits and the number of two-qubit gates, such as CNOT gates. To alleviate this problem, we aim to design efficient quantum circuits that would outperform the existing ones on the current noisy quantum devices. In this study, we designed a novel quantum circuit that reduces the required circuit depth and number of two-qubit entangling gates by about 60%, while retaining the accuracy of the ground state energies close to the chemical accuracy. Moreover, even in the presence of device noise, these novel shallower circuits yielded substantially low error rates than the existing approaches for predicting the ground state energies of molecules. By considering the umbrella inversion process in ammonia molecule as an example, we demonstrated the advantages of this new approach and estimated the energy barrier for the inversion process.

Understanding the bond dissociation energies (BDEs) of per- and polyfluoroalkyl substances (PFAS) helps in devising their efficient degradation pathways. However, there is only limited experimental data on the PFAS BDEs, and there are uncertainties associated with the BDEs computed using density functional theory. Although quantum chemical methods like the G4 composite method can provide highly accurate BDEs (< 1 kcal mol−1), they are limited to small system sizes. To address DFT's accuracy limitations and G4's system size constraints, we examined the connectivity-based hierarchy (CBH) scheme and found that it can provide BDEs that are reasonably close to the G4 accuracy while retaining the computational efficiency of DFT. To further improve the accuracy, we modified the CBH scheme and demonstrated that BDEs calculated using it have a mean-absolute deviation of 0.7 kcal mol−1 from G4 BDEs. To validate the reliability of this new scheme, we computed the ground state free energies of seven PFAS compounds and BDEs for 44 C–C and C–F bonds at the G4 level of theory. Our results suggest that the modified CBH scheme can accurately compute the BDEs of both small and large PFAS at near G4 level accuracy, offering promise for more effective PFAS degradation strategies.

Clathrate hydrates (CHs) are believed to exist within interstellar environments, potentially contributing to the preservation of diverse volatile compounds within icy bodies across the cosmos. In this study, using reflection absorption infrared spectroscopy, we show the formation of dimethyl ether (DME) CH from a vapor-deposited DME–water amorphous ice mixture. Experiments were conducted in an environment mimicking interstellar conditions: ultrahigh vacuum (P ∼ 5 × 10–10 mbar) and cryogenic conditions (T ∼ 10–150 K). Thermal annealing of the amorphous ice mixture to a higher temperature (T ∼ 125 K) resulted in the formation of CH. Quantum chemical calculations suggested the formation of 51264 cages of structure II CH. Subsequent investigations into the dissociation of DME CH unveiled its transformation into hexagonal ice, requiring a substantial activation energy of 68.04 kJ mol–1. Additionally, confirmation of the formation and dissociation of CH was supported by temperature-programmed desorption mass spectrometry. These results significantly advance our understanding of the existence of CHs under extreme conditions relevant to an interstellar medium.