scholarly journals An efficient and accurate decomposition of the Fermi operator

2008 ◽  
Vol 129 (2) ◽  
pp. 024707 ◽  
Author(s):  
Michele Ceriotti ◽  
Thomas D. Kühne ◽  
Michele Parrinello
Keyword(s):  
Fermi Operator

scholarly journals Mixed Precision Fermi-Operator Expansion on Tensor Cores from a Machine Learning Perspective

2021 ◽  
Author(s):  
Joshua Finkelstein ◽  
Justin S. Smith ◽  
Susan M. Mniszewski ◽  
Kipton Barros ◽  
Christian F. A. Negre ◽  
...  
Keyword(s):  
Machine Learning ◽  
Operator Expansion ◽  
Fermi Operator ◽  
Mixed Precision

Tight-Binding Molecular Dynamics of Ceramic Nanocrystals Using Pc-Based Parallel Machines

1999 ◽  
Vol 581 ◽  
Author(s):  
Kenji Tsuruta ◽  
Hiroo Totsuji ◽  
Chieko Totsuji
Keyword(s):  
Molecular Dynamics ◽  
Electronic Structures ◽  
Parallel Machines ◽  
Tight Binding ◽  
Expansion Method ◽  
Surface Structures ◽  
Electronic Density ◽  
Pc Cluster ◽  
Fermi Operator ◽  
Gap States

ABSTRACTEvolution of atomic and electronic structures of silicon-carbide (SiC) nanocrystals during sintering is investigated by a tight-binding molecular dynamics (TBMD) method. An O(N) algorithm (the Fermi-operator expansion method) is employed for calculating electronic contributions in the energy and forces. Simulations are performed on our eight-node parallel PC cluster. In a sintering simulation of aligned (no tilt or twist) SiC nanocrystals at T = 1000K, we find that a neck is formed promptly without formation of defects. Analyses of local electronic density-of-states (DOS) and effective charges reveal that unsaturated bonds exist only in grain surfaces accompanying the gap states. In the case of tilted (<122>) nanocrystals, surface structures formed before sintering affect significantly the grainboundary formation.

Improved Fermi operator expansion methods for fast electronic structure calculations

2003 ◽  
Vol 119 (8) ◽  
pp. 4117-4125 ◽  
Author(s):  
WanZhen Liang ◽  
Chandra Saravanan ◽  
Yihan Shao ◽  
Roi Baer ◽  
Alexis T. Bell ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Electronic Structure Calculations ◽  
Operator Expansion ◽  
Fermi Operator ◽  
Fast Electronic ◽  
Structure Calculations

A comparative study of the vibrational spectra of HCN in exact vibron model and in mean field approximation

2017 ◽  
Vol 95 (2) ◽  
pp. 130-135 ◽  
Author(s):  
Mahua Acharjee ◽  
Rupam Sen ◽  
Bidhan Mohanta
Keyword(s):  
Energy Levels ◽  
Mean Field ◽  
Field Approximation ◽  
Fermi Resonance ◽  
Mean Field Approximation ◽  
Local Mode ◽  
Vibrational States ◽  
Fermi Operator ◽  
Vibrational Levels ◽  
Casimir Operators

The aim of this work is to study the highly excited vibrational states of hydrogen cyanide HCN in the exact vibron model and with mean field approximation in the vibron model. Considering the U(4) ⊗ U(4) spectrum-generating algebra for linear triatomic molecules, the standard Hamiltonian is constructed using the linear and quadratic combination of Casimir operators. For higher order corrections, the quadratic contributions of Casimir operators are used to construct the Hamiltonian. Using this Hamiltonian the higher excited vibrational levels of HCN are calculated in the local mode approximation. The energy levels are observed as a function of vibron number N. The best fit is obtained for N = 184 (N1 = 139, N2 = 45) with root mean square (r.m.s.) deviation 5.598 cm−1. The intermodal coupling within the same polyad is studied and addressed properly by introducing Majorana operator. The r.m.s. deviation is then reduced to 4.755 cm−1. The modification is negligible, which indicates the local nature of HCN. In this work, 35 experimental levels are taken for fit, out of which only two sets of levels are accidentally degenerate. The Fermi resonances of the accidentally degenerate levels are studied using the Fermi operator and r.m.s. deviation becomes 4.835. The coefficient of Majorana and Fermi coupling for different levels are obtained by diagonalzing the Majorana and Fermi matrices for each polyad. The Majorana and Fermi matrices for each polyad are diagonalized with the MATRIX CALCULATOR program. The algebraic parameters are evaluated by a least square fit against the experimental data using MATLAB R2015a. Using this model, a set of energy levels is predicted up to 30 000 cm−1, with very good accuracy. HCN is chosen for this study, because, its vibrational states can be fairly described without any modification due to Fermi resonance. The fundamental vibrational levels of HCN are again calculated, using mean field approximation and compared to those obtained using the vibron model. A good agreement is observed.

scholarly journals Linear Scaling Pseudo Fermi-Operator Expansion for Fractional Occupation

2018 ◽  
Vol 15 (1) ◽  
pp. 190-200
Author(s):  
Susan M. Mniszewski ◽  
Romain Perriot ◽  
Emanuel H. Rubensson ◽  
Christian F. A. Negre ◽  
Marc J. Cawkwell ◽  
...  
Keyword(s):  
Linear Scaling ◽  
Operator Expansion ◽  
Fermi Operator

Parallel Tight-Binding Simulations of Nanophase Ceramics: Atomic and Electronic Transport at Grain Boundaries

2000 ◽  
Vol 653 ◽  
Author(s):  
Kenji Tsuruta ◽  
Hiroo Totsuji ◽  
Chieko Totsuji
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Electronic Transport ◽  
Parallel Machines ◽  
Tight Binding ◽  
Expansion Method ◽  
Nanocrystalline Silicon ◽  
Contact Angles ◽  
Neck Formation ◽  
Fermi Operator

AbstractWe report on tight-binding molecular dynamics (TBMD) of neck formation processes and atomistic and electronic diffusivity at grain boundaries of nanocrystalline silicon carbide. The TBMD simulations are based on an O(N) algorithm (the Fermi-operator expansion method) for calculating electronic contributions to energy and forces. The code has been fully parallelized on our PC-based parallel machines. The TBMD simulations of collision of SiC nanospheres show that the processes of neck formation depend strongly on contact angles between the two grains. Atomic diffusions are quite different in the necks formed with different angles. Also, the electronic transport property at grain boundary is investigated via a TB representation of an electronic diffusivity. A preliminary result on the diffusivity at a Σ=9 grain boundary of SiC indicates significant enhancement of electron mobility along the grain boundary.

scholarly journals Spectrum-splitting approach for Fermi-operator expansion in all-electron Kohn-Sham DFT calculations

2017 ◽  
Vol 95 (3) ◽  
Author(s):  
Phani Motamarri ◽  
Vikram Gavini ◽  
Kaushik Bhattacharya ◽  
Michael Ortiz
Keyword(s):  
Dft Calculations ◽  
Operator Expansion ◽  
Spectrum Splitting ◽  
Fermi Operator
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