Ab initio Total Energy Studies of the α-Cr2O3 (0001) and $(01\bar{1}2)$ Surfaces

1998 ◽  
Vol 05 (01) ◽  
pp. 337-340 ◽  
Author(s):  
C. Rehbein ◽  
F. Michel ◽  
N. M. Harrison ◽  
A. Wander
Keyword(s):  
Surface Layer ◽  
Ab Initio ◽  
Driving Force ◽  
Large Scale ◽  
Interlayer Spacing ◽  
Outermost Layer ◽  
Hartree Fock ◽  
Α Phase ◽  
Bulk Structure ◽  
The Ideal

The surface structure of the basal plane and of the thermodynamically most stable facet of the α phase of Cr 2 O 3 has been studied using periodic ab initio Hartree–Fock theory. The Cr-terminated (0001) surface, which is nonpolar but charged, is found to be stable. However, a large scale relaxation of the surface layer away from the ideal bulk-terminated structure has been found. The outermost layer of Cr 3+ ions moves inward toward the second layer of O 2- ions by nearly 50% of their original interlayer spacing. The [Formula: see text] surface, which is oxygen-terminated, is also nonpolar, and stable. Again an appreciable relaxation, with the top layer moving outward compared with the ideal bulk structure, is found. The driving force behind both effects is presumed to be mainly electrostatic.

Large- Scale ab initio Simulations of Fe-doped SrTiO3 Perovskites

2002 ◽  
Vol 731 ◽  
Author(s):  
R.A. Evarestov ◽  
R.I. Eglitis ◽  
S. Piskunov ◽  
E. A. Kotomin ◽  
G. Borstel
Keyword(s):  
Energy Level ◽  
Ab Initio ◽  
High Spin ◽  
Spin State ◽  
Large Scale ◽  
Covalent Bonding ◽  
Hartree Fock ◽  
Ab Initio Simulations ◽  
Displacement Mode ◽  
Jahn Teller

AbstractUsing the Unrestricted Hartree-Fock method and supercells containing up to 160 atoms, we calculated the energy level positions in the gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3. In agreement with experiment, the high spin (S=2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacement mode of the six nearest O ions which is a combination of the Jahn-Teller and breathing modes. A considerable covalent bonding between the Fe ion and four nearest O ions takes place.

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

Combustion Driven by Fragment-based Ab Initio Molecular Dynamics Simulation

2019 ◽  
Author(s):  
Liqun Cao ◽  
Jinzhe Zeng ◽  
Mingyuan Xu ◽  
Chih-Hao Chin ◽  
Tong Zhu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Large Scale ◽  
Methane Combustion ◽  
Combustion Method ◽  
Dynamics Simulation ◽  
Ab Initio Molecular Dynamics ◽  
Computational Time ◽  
Combustion Mechanism ◽  
Daily Lives

Combustion is a kind of important reaction that affects people's daily lives and the development of aerospace. Exploring the reaction mechanism contributes to the understanding of combustion and the more efficient use of fuels. Ab initio quantum mechanical (QM) calculation is precise but limited by its computational time for large-scale systems. In order to carry out reactive molecular dynamics (MD) simulation for combustion accurately and quickly, we develop the MFCC-combustion method in this study, which calculates the interaction between atoms using QM method at the level of MN15/6-31G(d). Each molecule in systems is treated as a fragment, and when the distance between any two atoms in different molecules is greater than 3.5 Å, a new fragment involved two molecules is produced in order to consider the two-body interaction. The deviations of MFCC-combustion from full system calculations are within a few kcal/mol, and the result clearly shows that the calculated energies of the different systems using MFCC-combustion are close to converging after the distance thresholds are larger than 3.5 Å for the two-body QM interactions. The methane combustion was studied with the MFCC-combustion method to explore the combustion mechanism of the methane-oxygen system.

Formation of surface layer of hydrogen in pure aluminum

2019 ◽  
Vol 484 (1) ◽  
pp. 56-60
Author(s):  
D. A. Indejtsev ◽  
E. V. Osipova
Keyword(s):  
Surface Layer ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Pure Aluminum ◽  
Hydrogen Atoms ◽  
Energy Characteristics ◽  
Aluminum Crystal

Hydrogen atom behavior in pure aluminum is described by ab initio modelling. All main energy characteristics of the system consisting of hydrogen atoms in a periodic aluminum crystal are found.

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βv/βe Ratio: Merocyanines

1998 ◽  
Vol 63 (9) ◽  
pp. 1295-1308 ◽  
Author(s):  
Benoît Champagne ◽  
Thierry Legrand ◽  
Eric A. Perpete ◽  
Olivier Quinet ◽  
Jean-Marie André
Keyword(s):  
Ab Initio ◽  
First Hyperpolarizability ◽  
Conjugated Molecules ◽  
Hartree Fock ◽  
Experimental Discovery ◽  
Conjugated Compounds ◽  
Molecular Frame

CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βv/βe ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βv/βe ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

THE FOREST FOR THE TREES: SOCIETY AND THE HOUSEHOLD IN EARLY MODERN EUROPE

1998 ◽  
Vol 41 (4) ◽  
pp. 1161-1172 ◽  
Author(s):  
JOEL F. HARRINGTON
Keyword(s):  
Large Scale ◽  
University Of Pennsylvania ◽  
Italian Renaissance ◽  
German History ◽  
Early Modern Europe ◽  
Cambridge University ◽  
Johns Hopkins University ◽  
Big Picture ◽  
To Come ◽  
The Ideal

Gender relations in German history: power, agency, and experience from the sixteenth to the twentieth century. Edited by Lynn Abrams and Elizabeth Harvey. London: UCL, 1996. Pp. x+262. ISBN 1-85728-485-2. £12.95.Adultery and divorce in Calvin's Geneva. By Robert M. Kingdon. Cambridge, Mass., and London: Harvard UP, 1995. Pp. ix+214. ISBN 0-674-00520-1 (hb). £18.50.Housecraft and statecraft: domestic service in Renaissance Venice, 1400–1600. By Dennis Romano. Baltimore: Johns Hopkins University Press, 1996. Pp. xxvi+333. ISBN 0-8018-5288-9. £37.00.The European nobility, 1400–1800. By Jonathan Dewald. New approaches to European history, ix. Cambridge: Cambridge University Press, 1996. Pp. xvii+209. ISBN 0-521-42528-x (pb). £12.95.Garden and grove: the Italian Renaissance garden in the English imagination, 1600–1750. By John Dixon Hunt. Philadelphia: University of Pennsylvania, 1996. Pp. xix+268. ISBN 0-8122-1604-0 (pb). £23.50.Like an ancient woodsman or a guide through the Amazonian jungle, the ideal historian possesses at least two kinds of expertise: enough familiarity with the general terrain to plan successful expeditions and enough experience in the field to make inevitable adjustments to ‘the big picture’ when underway. Of course in the real world (of both geography and history) the tasks of exploration and cartography are often bifurcated, without necessarily disastrous results. The historian who is equally skilled at both close-up description and large-scale theorizing is consequently celebrated as a rare and valued anomaly. Meanwhile, for most of us stumbling scouts, the world beyond our familiar trails remains largely one of learned lore, with connections to our own limited forays often vague at best. Unless, of course, we are fortunate enough to come across something which provides an almost magical link between the narrow and the wide, the micro and the macro.

Polaronic and Bipolaronic Enhancement of Second Hyperpolarizabilities in Dithienyl Polyenes from Ab Initio Quantum Methods

1999 ◽  
Vol 597 ◽  
Author(s):  
Steven Trohalaki ◽  
Robert J. Zellmer ◽  
Ruth Pachter
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Valence Bond ◽  
Closed Shell ◽  
Functional Theory ◽  
Molecular Conformations ◽  
Hartree Fock ◽  
Molecular Charge ◽  
Field Methodology ◽  
Moller Plesset

AbstractSpangler and He [1,2] have shown that dithienyl polyenes form extremely stable bipolaronic dications when oxidatively doped in solution. Previous theoretical studies applied empirical methods to predict bipolaronic enhancement of hyperpolarizabilities for simple polyenes [3,4]. Here, we employ density functional theory to optimize the gas-phase molecular conformations of neutral, cationic, and dicationic forms of a series of dithienyl polyenes, where the number of ethene units, N, is varied from 1–5. Ab initio Hartree-Fock, generalized valence bond, configuration interaction, and Møller-Plesset calculations demonstrate that the dications are farily well described with a closed shell and therefore have little biradicaloid character. Second hyperpolarizabilities, γ, are subsequently calculated using ab initio Hartree-Fock theory and a finite field methodology. As expected, γ increases with the number of ethene units for a given molecular charge. The cations also show the largest increase in γ with N. For a given value of N, the cations display the largest γ values. However, if we treat the dication as a triplet, which might be present in solution, then it displays the largest γ.

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