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- Ahmadzadeh, Karan, et al.
(författare)
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Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the self-consistent field approximation
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:2
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Tidskriftsartikel (refereegranskat)abstract
- Within the self-consistent field approximation, computationally tractable expressions for the isotropic second-order hyperpolarizability have been derived and implemented for the calculation of two-photon absorption cross sections. The novel tensor average formulation presented in this work allows for the evaluation of isotropic damped cubic response functions using only similar to 3.3% (one-photon off-resonance regions) and similar to 10% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of the two-photon absorption cross section in the one-photon off-resonance and resonance regions are provided for alanine-tryptophan and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene. Furthermore, a benchmark set of 22 additional small- and medium-sized organic molecules is considered. In all these calculations, a quantitative assessment is made of the reduced and approximate forms of the cubic response function in the one-photon off-resonance regions and results demonstrate a relative error of less than similar to 5% when using the reduced expression as compared to the full form of the isotropic cubic response function.
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- Brand, Manuel, et al.
(författare)
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Efficient and Parallel Implementation of Real and Complex Response Functions Employing the Second-Order Algebraic-Diagrammatic Construction Scheme for the Polarization Propagator
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 20:1, s. 103-113
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Tidskriftsartikel (refereegranskat)abstract
- We present the implementation of an efficient matrix-folded formalism for the evaluation of complex response functions and the calculation of transition properties at the level of the second-order algebraic-diagrammatic construction (ADC(2)) scheme. The underlying algorithms, in combination with the adopted hybrid MPI/OpenMP parallelization strategy, enabled calculations of the UV/vis spectra of a guanine oligomer series ranging up to 1032 contracted basis functions, thereby utilizing vast computational resources from up to 32,768 CPU cores. Further analysis of the convergence behavior of the involved iterative subspace algorithms revealed the superiority of a frequency-separated treatment of response equations even for a large spectral window, including 101 frequencies. We demonstrate the applicability to general quantum mechanical operators by the first reported electronic circular dichroism spectrum calculated with a complex polarization propagator approach at the ADC(2) level of theory.
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- Brand, Manuel, et al.
(författare)
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Efficient parallel implementation of complex response functions employing the algebraic-diagrammatic construction scheme
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present the derivation and implementation of an efficient matrix-folded formalism for the evaluation of complex response functions at the level of the second-order algebraic-diagrammatic construction ADC(2) scheme. The adopted hybrid MPI/OpenMP parallelization strategy enables the utilization of vast computational resources without significant performance losses as demonstrated by consistent size-scalings for the computationally most demanding steps obtained from calculations of the UV/vis spectra of a guanine oligomer series ranging up to 1,032 contracted basis functions. Further analysis of the convergence behavior of the involved iterative subspace algorithm revealed the superiority of a frequency-separated treatment of response equations even for a large spectral window including 101 frequencies. We demonstrate the applicability to general quantum mechanical operators by the first reported electric circular dichroism spectrum calculated with the complex polarization propagator approach at the ADC(2) level of theory.
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- Brand, Manuel
(författare)
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Implementation of complex polarization propagator theory for linear response properties of large molecular systems
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since its beginning, the remarkable development from the first commercially available computers toward exascale supercomputers just within the span of a lifetime has been closely intertwined with the perpetual quest for the utilization of the arising computing power for the avail of theoretical chemistry. With the aim of further pushing the limits of computationally accessible molecular system sizes, this thesis includes the presentation of programming efforts, which brought forth two quantum chemical software codes, as well as a range of ab initio studies on carbon-based systems, enabled by the former.The VeloxChem and Gator programs, developed for spectroscopy simulations at the level of density-functional theory (DFT) and correlated wave function methods, respectively, employ a hybrid message passing interface (MPI)/open multiprocessing (OpenMP) parallelization scheme embedded in a modular program structure written in a Python/C++ layered fashion for the execution in contemporary high-performance computing (HPC) environments. Included numerical solvers for the evaluation of real and complex linear response functions in combination with the parallel construction of auxiliary Fock matrices enable the efficient calculation of one-photon absorption or electronic circular dichroism (CD) spectra in the ultraviolet/visible (UV/vis) or X-ray spectral region, as well as van der Waals C6 dispersion coefficients.Employing the VeloxChem program in two comprehensive investigations, the C6 dispersion coefficients of carbon fullerenes up to a system size of C540 and the CD spectra of carbohelicenes ranging from CH[5] to CH[30] have been calculated at the DFT level of theory. The revealed non-additive scaling with respect to the number of carbon atoms of N2.2 in the former and nontrivial CD band progressions, arguably linked to the number of overlapping layers in the helical conjugated systems, in the latter rectify the current conception in their respective fields.In a benchmark for the Gator program on a series of guanine oligomers, the full UV/vis spectrum for a tetrad was calculated at the level of a second-order algebraic-diagrammatic construction (ADC(2)) scheme in just under 15 hours by efficient employment of 32,768 central processing unit (CPU) cores.Exceeding the limit of 10,000 and 1,000 contracted basis functions for a treatment with the DFT and ADC(2) methods, respectively, these practical examples demonstrate the capability of VeloxChem and Gator to harness vast computational resources made available by contemporary and future HPC systems and thereby routinely address scopes of system sizes that were previously out of reach.
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- Brand, Manuel, et al.
(författare)
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Nontrivial spectral band progressions in electronic circular dichroism spectra of carbohelicenes revealed by linear response calculations
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:32, s. 19321-19332
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that contemporary computational resources allow for accurate theoretical studies of systems matching recent advances in experimental helicene chemistry. Concerned with first-principles calculations of carbohelicenes, our work surpasses CH[12] as the largest system investigated to date and unravels trends in the electronic structure of the low-lying states of the homologous series. Utilizing a highly efficient implementation of linear response algorithms, we present electronic circular dichroism (CD) spectra of carbohelicenes ranging from CH[5] to CH[30] at the level of Kohn-Sham density-functional theory. Our results for a systematic increase in system size show the emergence of new CD bands that subsequently rise to intensities dominating the spectrum. The spectral band progressions exhibit a periodicity directly linked to the number of overlapping layers of conjugation. While our findings rectify the current understanding of the electronic structure of carbohelicenes, they also serve as a general call for caution regarding the extrapolation of trends from small system ranges.
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- Brand, Manuel, et al.
(författare)
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Size-dependent polarizabilities and van der Waals dispersion coefficients of fullerenes from large-scale complex polarization propagator calculations
- 2021
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Ingår i: Journal of Chemical Physics. - : AMER INST PHYSICS. - 0021-9606 .- 1089-7690. ; 154:7
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Tidskriftsartikel (refereegranskat)abstract
- While the anomalous non-additive size-dependencies of static dipole polarizabilities and van der Waals C-6 dispersion coefficients of carbon fullerenes are well established, the widespread reported scalings for the latter (ranging from N-2.2 to N-2.8) call for a comprehensive first-principles investigation. With a highly efficient implementation of the linear complex polarization propagator, we have performed Hartree-Fock and Kohn-Sham density functional theory calculations of the frequency-dependent polarizabilities for fullerenes consisting of up to 540 carbon atoms. Our results for the static polarizabilities and C-6 coefficients show scalings of N-1.2 and N-2.2, respectively, thereby deviating significantly from the previously reported values obtained with the use of semi-classical/empirical methods. Arguably, our reported values are the most accurate to date as they represent the first ab initio or first-principles treatment of fullerenes up to a convincing system size.
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- Ellinghaus, David, et al.
(författare)
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Association between variants of PRDM1 and NDP52 and Crohn's disease, based on exome sequencing and functional studies
- 2013
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Ingår i: Gastroenterology. - : Elsevier BV. - 0016-5085 .- 1528-0012. ; 145:2, s. 339-347
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND & AIMS: Genome-wide association studies (GWAS) have identified 140 Crohn's disease (CD) susceptibility loci. For most loci, the variants that cause disease are not known and the genes affected by these variants have not been identified. We aimed to identify variants that cause CD through detailed sequencing, genetic association, expression, and functional studies.METHODS: We sequenced whole exomes of 42 unrelated subjects with CD and 5 healthy subjects (controls) and then filtered single nucleotide variants by incorporating association results from meta-analyses of CD GWAS and in silico mutation effect prediction algorithms. We then genotyped 9348 subjects with CD, 2868 subjects with ulcerative colitis, and 14,567 control subjects and associated variants analyzed in functional studies using materials from subjects and controls and in vitro model systems.RESULTS: We identified rare missense mutations in PR domain-containing 1 (PRDM1) and associated these with CD. These mutations increased proliferation of T cells and secretion of cytokines on activation and increased expression of the adhesion molecule L-selectin. A common CD risk allele, identified in GWAS, correlated with reduced expression of PRDM1 in ileal biopsy specimens and peripheral blood mononuclear cells (combined P = 1.6 x 10(-8)). We identified an association between CD and a common missense variant, Val248Ala, in nuclear domain 10 protein 52 (NDP52) (P = 4.83 x 10(-9)). We found that this variant impairs the regulatory functions of NDP52 to inhibit nuclear factor kappa B activation of genes that regulate inflammation and affect the stability of proteins in Toll-like receptor pathways.CONCLUSIONS: We have extended the results of GWAS and provide evidence that variants in PRDM1 and NDP52 determine susceptibility to CD. PRDM1 maps adjacent to a CD interval identified in GWAS and encodes a transcription factor expressed by T and B cells. NDP52 is an adaptor protein that functions in selective autophagy of intracellular bacteria and signaling molecules, supporting the role of autophagy in the pathogenesis of CD.
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