arXiv subjects

Manoar Hossain

Publications and source records attributed to Manoar Hossain.

10 recordsLinked to original sources

arXiv2026

A Unified Dielectric-Dependent Hybrid Functional for Accurate Band Gaps across Dimensions

Predicting fundamental band gaps across material classes and dimensionalities remains a central challenge in electronic-structure theory. Here, we show that intrinsic dielectric screening provides a unified control parameter for nonlocal exchange from bulk to low-dimensional and heterogeneous materials. We introduce a geometry-independent dielectric response and incorporate it self-consistently into a nonempirical screened-dielectric-dependent hybrid functional. Benchmarks for 100 materials spanning bulk, two-dimensional, one-dimensional, and mixed-dimensional systems show near-GW accuracy at the computational cost of generalized Kohn-Sham theory. These results reveal a screening-exchange-gap relation in which reduced dimensionality weakens intrinsic dielectric screening, strengthens nonlocal exchange, and drives the opening of fundamental gaps.

cond-mat.mtrl-sci↗

arXiv2026

An exciting approach to theoretical spectroscopy

Theoretical spectroscopy, and more generally, electronic-structure theory, are powerful concepts for describing the complex many-body interactions in materials. They comprise a variety of methods that can capture all aspects, from ground-state properties to lattice excitations to different types of light-matter interaction, including time-resolved variants. Modern electronic-structure codes implement either a few or several of these methods. Among them, exciting is an all-electron full-potential package that has a very rich portfolio of all levels of theory, with a particular focus on excitations. It implements the linearized augmented planewave plus local orbital (LAPW+LO) basis, which is known as the gold standard for solving the Kohn-Sham equations of density-functional theory (DFT). Based on this, it also offers benchmark-quality results for a wide range of excited-state methods. In this review, we provide a comprehensive overview of the features implemented in exciting in recent years, accompanied by short summaries on the state of the art of the underlying methodologies. They comprise DFT and time-dependent DFT (TDDFT), density-functional perturbation theory (DFPT) for phonons and electron-phonon coupling, and many-body perturbation theory in terms of the $GW$ approach and the Bethe-Salpeter equation (BSE). Moreover, exciting can handle resonant inelastic x-ray scattering (RIXS), pump-probe spectroscopy as well as exciton-phonon coupling (EXPC). Finally, we cover workflows and a view on data and machine learning (ML). All aspects are demonstrated with examples for scientifically relevant materials.

cond-mat.mtrl-sci↗

arXiv2025

Otus Supercomputer

Otus is a high-performance computing cluster that was launched in 2025 and is operated by the Paderborn Center for Parallel Computing (PC2) at Paderborn University in Germany. The system is part of the National High Performance Computing (NHR) initiative. Otus complements the previous supercomputer Noctua 2, offering approximately twice the computing power while retaining the three node types that were characteristic of Noctua 2: 1) CPU compute nodes with different memory capacities, 2) high-end GPU nodes, and 3) HPC-grade FPGA nodes. On the Top500 list, which ranks the 500 most powerful supercomputers in the world, Otus is in position 164 with the CPU partition and in position 255 with the GPU partition (June 2025). On the Green500 list, ranking the 500 most energy-efficient supercomputers in the world, Otus is in position 5 with the GPU partition (June 2025). This article provides a comprehensive overview of the system in terms of its hardware, software, system integration, and its overall integration into the data center building to ensure energy-efficient operation. The article aims to provide unique insights for scientists using the system and for other centers operating HPC clusters. The article will be continuously updated to reflect the latest system setup and measurements.

cs.DC↗

arXiv2025

Advancing excited-state properties of two-dimensional materials using a dielectric-dependent hybrid functional

Predicting accurate band gaps and optical properties of lower-dimensional materials, including two-dimensional van der Waals (vdW) materials and their heterostructures, remains a challenge within density functional theory (DFT) due to their unique screening compared to their bulk counterparts. Additionally, accurate treatment of the dielectric response is crucial for developing and applying screened-exchange dielectric-dependent range-separated hybrid functionals (SE-DD-RSH) for vdW materials. In this work, we introduce a SE-DD-RSH functional to the 2D vdW materials like MoS2, WS2, hBN, black phosphorus (BP), and \b{eta}-InSe. By accounting for in-plane and out-of-plane dielectric responses, our method achieves accuracy comparable to advanced many-body techniques like G0 W0 and BSE@G0 W0 at a lower computational cost. We demonstrate improved band gap predictions and optical absorption spectra for both bulk and layered structures, including some heterostructures like MoS2/WS2 . This approach offers a practical and precise tool for exploring electronic and optical phenomena in 2D materials, paving the way for efficient computational studies of layered systems.

cond-mat.mtrl-sci↗

arXiv2024

Accurate and efficient prediction of the band gaps and optical spectra of chalcopyrite semiconductors from a non-empirical range-separated dielectric-dependent hybrid: Comparison with many-body perturbation theory

The accurate prediction of electronic and optical properties in chalcopyrite semiconductors has been a persistent challenge for density functional theory (DFT) based approaches. Addressing this issue, we demonstrate that very accurate results can be obtained using a non-empirical screened dielectric-dependent hybrid (DDH) functional. This novel approach showcases its impressive capability to accurately determine band gaps, optical bowing parameters, and optical absorption spectra for chalcopyrite systems. What sets the screened DDH functional apart is its adeptness in capturing the many-body physics associated with highly localized $d$ electrons. Notably, the accuracy is comparable to the many-body perturbation based methods (such as $G_0W_0$ or its various approximations for band gaps and Bethe-Salpeter equation (BSE) on the top of the $G_0W_0$ or its various approximations for optical spectra) with less computational cost, ensuring a more accessible application across various research domains. The present results show the predictive power of the screened DDH functional, pointing toward promising applications where computational efficiency and predictive accuracy are crucial considerations. Overall, the screened DDH functional offers a compelling balance between cost-effectiveness and precision, making it a valuable tool for future endeavors in exploring chalcopyrite semiconductors and beyond.

cond-mat.mtrl-sci↗

arXiv2023

Optical excitation from anti-causally corrected real-time dynamics in a minimal basis

Here we demonstrate workably accurate estimation of optical excitation threshold for large systems comprising of hundreds of atoms through an anti-causally corrected(ACC) real-time dynamics(RTD) approach implemented in a minimal tight-binding basis constituted by the directed hybrid atomic Wannier orbitals. A correction to the Hamiltonian is applied anti-causally at all time steps to account for electron-hole interaction using the density-density response function. Minimality of basis and ease of transferability of parameters to large systems arises from the directed nature of the Wannierized hybrid basis orbitals used.With self-energy corrected TB parameters evaluated at the DFT + G 0 W 0 level, the proposed ACC-RTD scheme can be systematically parametrized to render optical excitation threshold for systems of experimentally realizable length-scales through inexpensive computation.

cond-mat.mtrl-sci↗

arXiv2022

Maximally valent orbitals in systems with non-ideal bond-angles

In pursuit of a minimal basis for systems with non-ideal bond angles, in this work we try to pinpoint the exact orientation of the major overlapping orbitals along the nearest neighbouring coordination segments in a given system such that they maximally represent the covalent interactions through out the system. We compute Mayer's bond order, akin to the Wiberg's bond index, in the basis of atomic Wannier orbitals with customizable non-degenerate hybridization constructed from first principles, in a representative variety of molecules and layered systems. We put them in perspective with unbiased maximally localized descriptions of bonding and non-bonding orbitals, and energetics to tunneling of electrons through them between nearest neighbours, to describe the different physical aspects of covalent interactions, which are not necessarily represented by a single unique set of atomic or bonding orbitals.

cond-mat.mtrl-sci↗

arXiv2021

Self-energy corrected tight binding parameters for few p-block semiconductors in the hybridized atomic orbital basis constructed from first principles

We present self-energy corrected tight-binging(TB) parameters in the basis of the directed hybridised atomic orbitals constructed from first principles, for nano-diamonds as well as bulk diamond and zinc blende structures made of elements of group 13, 14 and 15 in the 2p, 3p and 4p blocks. With increasing principal quantum number of frontier orbitals, the lowering of self-energy corrections(SEC) to the band-gap and consequently to the dominant inter-atomic TB parameters, is much faster in bulk than in nano-diamonds and hence not transferable from bulks to nano-structures. However, TB parameters transfered from smaller nano-diamonds to much larger ones exclusively through mapping of neighbourhoods of atoms not limited to nearest neighbours, are found to render HOMO-LUMO gaps of the larger nano-diamonds with few hundreds of atoms in good agreement with their explicitly computed values at the DFT as well as DFT+G0W0 levels. TB parameters and their SEC are found to vary significantly from 2p to 3p block but negligibly from 3p to 4p, while varying rather slowly within each block, implying the possibility of transfer of SEC across block with increasing principal quantum number. The demonstrated easy transferability of self-energy corrected TB parameters in the hybrid orbital basis thus promises computationally inexpensive estimation of quasi-particle electronic structure of large finite systems with thousands of atoms.

cond-mat.mtrl-sci↗

arXiv2021

Hybrid atomic orbital basis from first principles: Bottom-up mapping of self-energy correction to large covalent systems

Construction of hybrid atomic orbitals is proposed as the approximate common eigen states of finite first moment matrices. Their hybridization and orientation can be a-priori tunned as per their anticipated neighbourhood. Their Wannier function counterparts constructed from the Kohn-Sham(KS) single particle states constitute an orthonormal multi-orbital tight-binding(TB) basis resembling hybrid atomic-orbitals locked to their immediate atomic neighborhood, while spanning the subs-space of KS states. The proposed basis thus not only renders predominantly single TB parameters from first-principles for each nearest neighbour bonds involving no more than two orbitals irrespective of their orientation, but also facilitate an easy route for transfer of such TB parameters across isostructural systems exclusively through mapping of neighbourhoods and projection of orbital charge centres. With hybridized 2s,2p and 3s,3p valence electrons, the spatial extent of self-energy correction(SEC) to TB parameters in the proposed basis are found to be localized mostly within the third nearest neighbourhood, thus allowing effective transfer of self-energy corrected TB parameters from smaller reference systems to much larger target systems, with nominal additional computational cost beyond that required for explicit computation of SEC in the reference systems. The proposed approach promises inexpensive estimation of quasi-particle structure of large covalent systems with workable accuracy.

cond-mat.mtrl-sci↗

arXiv2020

Transferability of self-energy correction in tight-binding basis constructed from first principles

We demonstrate in this work the transferability of self-energy(SE) correction(SEC) of Kohn-Sham(KS) single particle states from smaller to larger systems, when mapped through localized orbitals constructed from the KS states. The approach results in a SE corrected TB framework, within which, the mapping of SEC of TB parameters is found to be transferable from smaller to larger systems of similar morphology, leading to a computationally inexpensive approach for estimation of SEC in large systems with reasonably high accuracy. The scheme has been demonstrated in insulating, semiconducting and magnetic nanoribbons of graphene and hexagonal boron nitride, where SEC tends to strengthen the individual pi bonds, leading to transfer of charge from edge to bulk. Additionally in magnetic bipartite systems SEC tends to enhance inter-sublattice spin separation. The proposed scheme thus promises to enable estimation of SEC of band-gaps of large systems without needing to explicitly calculate SEC of KS single particle levels which can be computationally prohibitively expensive.

cond-mat.mtrl-sci↗