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 The Effect of Hartree-Fock Exchange on Scaling Relations and Reaction Energetics for C–H Activation Catalysts

2021 ◽  
Author(s):  
Vyshnavi Vennelakanti ◽  
Aditya Nandy ◽  
Heather Kulik
Keyword(s):  
Spin State ◽  
Density Functional ◽  
Large Scale ◽  
Predictive Power ◽  
Minimum Energy ◽  
Poor Performance ◽  
Closed Shell ◽  
Open Shell ◽  
Methanol Conversion ◽  
Hartree Fock

<p>High-throughput computational catalyst studies are typically carried out using density functional theory (DFT) with a single, approximate exchange-correlation functional. In open shell transition metal complexes (TMCs) that are promising for challenging reactions (e.g., C–H activation), the predictive power of DFT has been challenged, and properties are known to be strongly dependent on the admixture of Hartree-Fock (HF) exchange. We carry out a large-scale study of the effect of HF exchange on the predicted catalytic properties of over 1,200 mid-row (i.e., Cr, Mn, Fe, Co) 3<i>d </i>TMCs for direct methane-to-methanol conversion. Reaction energetic sensitivities across this set depend both on the catalytic rearrangement and ligand chemistry of the catalyst. These differences in sensitivities change both the absolute energetics predicted for a catalyst and its relative performance. Previous observations of the poor performance of global linear free energy relationships (LFERs) hold with both semi-local DFT widely employed in heterogeneous catalysis and hybrid DFT. Narrower metal/oxidation/spin-state specific LFERs perform better and are less sensitive to HF exchange than absolute reaction energetics, except in the case of some intermediate/high-spin states. Importantly, the interplay between spin-state dependent reaction energetics and exchange effects on spin-state ordering means that the choice of DFT functional strongly influences whether the minimum energy pathway is spin-conserved. Despite these caveats, LFERs involving catalysts that can be expected to have closed shell intermediates and low-spin ground states retain significant predictive power.</p>

Dynamic Jahn–Teller Effect in the Metastable High-Spin State of Solvated [Fe(terpy)2]2+

2015 ◽  
Vol 119 (6) ◽  
pp. 3312-3321 ◽  
Author(s):  
X. Zhang ◽  
M. L. Lawson Daku ◽  
J. Zhang ◽  
K. Suarez-Alcantara ◽  
G. Jennings ◽  
...  
Keyword(s):  
High Spin ◽  
Spin State ◽  
High Spin State ◽  
Teller Effect ◽  
Jahn Teller ◽  
Jahn Teller Effect

scholarly journals Large-scale ab initio simulations based on systematically improvable atomic basis

2016 ◽  
Vol 112 ◽  
pp. 503-517 ◽  
Author(s):  
Pengfei Li ◽  
Xiaohui Liu ◽  
Mohan Chen ◽  
Peize Lin ◽  
Xinguo Ren ◽  
...  
Keyword(s):  
Ab Initio ◽  
Large Scale ◽  
Ab Initio Simulations

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>

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.

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>

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