Regularized and Renormalized Many-Body Techniques for Describing Correlated Molecular Systems: A Coupled-Cluster Perspective

2018 ◽  
pp. 3-45 ◽  
Author(s):  
Karol Kowalski ◽  
Jiri Brabec ◽  
Bo Peng
Keyword(s):  
Coupled Cluster ◽  
Many Body ◽  
Molecular Systems ◽  
Body Techniques

Double Precision Is Not Needed for Many-Body Calculations: New Conventional Wisdom

2018 ◽  
Author(s):  
Pavel Pokhilko ◽  
Evgeny Epifanovsky ◽  
Anna I. Krylov
Keyword(s):  
Large Scale ◽  
Computation Time ◽  
Coupled Cluster ◽  
Double Precision ◽  
Many Body ◽  
Single Precision ◽  
Parallel Performance ◽  
Point Representation ◽  
Electron Repulsion Integrals ◽  
Cluster Methods

Using single precision floating point representation reduces the size of data and computation time by a factor of two relative to double precision conventionally used in electronic structure programs. For large-scale calculations, such as those encountered in many-body theories, reduced memory footprint alleviates memory and input/output bottlenecks. Reduced size of data can lead to additional gains due to improved parallel performance on CPUs and various accelerators. However, using single precision can potentially reduce the accuracy of computed observables. Here we report an implementation of coupled-cluster and equation-of-motion coupled-cluster methods with single and double excitations in single precision. We consider both standard implementation and one using Cholesky decomposition or resolution-of-the-identity of electron-repulsion integrals. Numerical tests illustrate that when single precision is used in correlated calculations, the loss of accuracy is insignificant and pure single-precision implementation can be used for computing energies, analytic gradients, excited states, and molecular properties. In addition to pure single-precision calculations, our implementation allows one to follow a single-precision calculation by clean-up iterations, fully recovering double-precision results while retaining significant savings.

Application of multireference linearized coupled-cluster theory to atomic and molecular systems

2018 ◽  
Vol 17 (02) ◽  
pp. 1850016 ◽  
Author(s):  
Jiang Yi ◽  
Feiwu Chen
Keyword(s):  
Ground State ◽  
Basis Sets ◽  
Coupled Cluster ◽  
Vibration Frequencies ◽  
Electron Affinities ◽  
Proton Affinities ◽  
Coupled Cluster Theory ◽  
Molecular Systems ◽  
Ground State Energies ◽  
Second Order Perturbation Theory

Applications of the multireference linearized coupled-cluster single-doubles (MRLCCSD) to atomic and molecular systems have been carried out. MRLCCSD is exploited to calculate the ground-state energies of HF, H2O, NH3, CH4, N2, BF, and C2with basis sets, cc-pVDZ, cc-pVTZ and cc-pVQZ. The equilibrium bond lengths and vibration frequencies of HF, HCl, Li2, LiH, LiF, LiBr, BH, and AlF are computed with MRLCCSD and compared with the experimental data. The electron affinities of F and CH as well as the proton affinities of H2O and NH3are also calculated with MRLCCSD. These results are compared with the results produced with second-order perturbation theory, linearized coupled-cluster doubles (LCCD), coupled-cluster doubles (CCD), coupled-cluster singles and doubles (CCSD), CCSD with perturbative triples correction (CCSD(T)). It is shown that all results obtained with MRLCCSD are reliable and accurate.

Between Accuracy and Manageability: Computational Imperatives in Quantum Chemistry

2009 ◽  
Vol 39 (1) ◽  
pp. 32-62 ◽  
Author(s):  
Buhm Soon Park
Keyword(s):  
Quantum Chemistry ◽  
Early Years ◽  
Many Body ◽  
Molecular Systems ◽  
Technological Improvement ◽  
Computational Work ◽  
Human Labor ◽  
History Of ◽  
History Of Quantum Theory ◽  
Theory And Experiment

This article explores the place of computation in the history of quantum theory by examining the development of several approximation methods to solve the Schröödinger equation without using empirical information, as these were worked out in the years from 1927 to 1933. These ab initio methods, as they became known, produced the results that helped validate the use of quantum mechanics in many-body atomic and molecular systems, but carrying out the computations became increasingly laborious and difficult as better agreement between theory and experiment was pursued and more complex systems were tackled. I argue that computational work in the early years of quantum chemistry shows an emerging practice of theory that required human labor, technological improvement (computers), and mathematical ingenuity.

scholarly journals Colloidal interactions and unusual crystallization versus de-mixing of elastic multipoles formed by gold mesoflowers

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ye Yuan ◽  
Mykola Tasinkevych ◽  
Ivan I. Smalyukh
Keyword(s):  
Self Assembly ◽  
Energy Minimization ◽  
Topological Defects ◽  
High Order ◽  
Colloidal System ◽  
Many Body ◽  
Molecular Systems ◽  
Colloidal Interactions ◽  
Many Body Interactions ◽  
Different Order

AbstractColloidal interactions in nematic liquid crystals can be described as interactions between elastic multipoles that depend on particle shape, topology, chirality, boundary conditions and induced topological defects. Here, we describe a nematic colloidal system consisting of mesostructures of gold capable of inducing elastic multipoles of different order. Elastic monopoles are formed by relatively large asymmetric mesoflower particles, for which gravity and elastic torque balancing yields monopole-type interactions. High-order multipoles are instead formed by smaller mesoflowers with a myriad of shapes corresponding to multipoles of different orders, consistent with our computer simulations based on free energy minimization. We reveal unexpected many-body interactions in this colloidal system, ranging from de-mixing of elastic monopoles to a zoo of unusual colloidal crystals formed by high-order multipoles like hexadecapoles. Our findings show that gold mesoflowers may serve as a designer toolkit for engineering colloidal interaction and self-assembly, potentially exceeding that in atomic and molecular systems.

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