Constrained-Orbital Density Functional Theory. Computational Method and Applications to Surface Chemical Processes

2017 ◽  
Vol 13 (8) ◽  
pp. 3561-3574 ◽  
Author(s):  
Craig P. Plaisance ◽  
Rutger A. van Santen ◽  
Karsten Reuter
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Chemical Processes ◽  
Computational Method ◽  
Surface Chemical ◽  
Functional Theory ◽  
Orbital Density

Further developments in the local-orbital density-functional-theory tight-binding method

2001 ◽  
Vol 64 (19) ◽  
Author(s):  
James P. Lewis ◽  
Kurt R. Glaesemann ◽  
Gregory A. Voth ◽  
Jürgen Fritsch ◽  
Alexander A. Demkov ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Tight Binding ◽  
Functional Theory ◽  
Tight Binding Method ◽  
Orbital Density

Electronic Structure, Nonlinear Optical Properties, and Vibrational Analysis of Ethyl benzoate by Density Functional Theory

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Tanveer Hasan ◽  
P. K. Singh
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Vibrational Analysis ◽  
Ethyl Benzoate ◽  
Computational Method ◽  
Basis Set ◽  
Vibrational Modes ◽  
Normal Coordinate ◽  
Functional Theory ◽  
Vibrational Bands

This work deals with the vibrational spectroscopy of Ethyl benzoate (C9H10O2). The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) using standard HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods and basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

Van der Waals forces in the local-orbital Density Functional Theory

2005 ◽  
Vol 70 (3) ◽  
pp. 355-361 ◽  
Author(s):  
M. A Basanta ◽  
Y. J Dappe ◽  
J Ortega ◽  
F Flores
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Functional Theory ◽  
Orbital Density

scholarly journals Molecular dynamics with constrained nuclear electronic orbital density functional theory: Accurate vibrational spectra from efficient incorporation of nuclear quantum effects

2021 ◽  
Author(s):  
Xi Xu ◽  
Zehua Chen ◽  
Yang Yang
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Vibrational Spectra ◽  
Density Functional ◽  
Molecular Simulations ◽  
Quantum Effects ◽  
Functional Theory ◽  
Chemical And Biological Systems ◽  
Nuclear Quantum Effects ◽  
Orbital Density

Nuclear quantum effects play a crucial role in many chemical and biological systems involving hydrogen atoms yet are difficult to include in practical molecular simulations. In this Letter, we combine our recently developed methods of constrained nuclear-electronic orbital density functional theory (cNEO-DFT) and constrained minimized energy surface molecular dynamics (CMES-MD) to create a new method for accurately and efficiently describing nuclear quantum effects in molecular simulations. Using this new method, dubbed cNEO-MD, the vibrational spectra of a set of small molecules are calculated and compared with those from conventional ab initio molecular dynamics (AIMD) as well as from experiments. With the same formal scaling, cNEO-MD greatly outperforms AIMD in describing the vibrational modes with significant hydrogen motion characters, demonstrating the promise of cNEO-MD for simulating chemical and biological systems with significant nuclear quantum effects.

Subatomic Resolution in Noncontact Atomic Force Microscopy: Electron Cloud Interactions or Harmonics Processing Artifacts?

2012 ◽  
Author(s):  
C. Alan Wright ◽  
Santiago D. Solares
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Electron Cloud ◽  
Computational Method ◽  
Functional Theory ◽  
Force Microscopy ◽  
Atomic Force ◽  
Imaging Artifacts ◽  
The Individual ◽  
Tungsten Tip

In 2004 Hembacher et al. [Science 305, 380–383 (2004)] reported higher harmonics AFM images of a graphite surface acquired using a tungsten tip which revealed subatomic features. These features were interpreted as the signature of electron bonding lobes at the tip apex atom. We recently applied a computational method based on density functional theory to simulate the images of Hembacher et al. and found that features of subatomic size can indeed be observed under ideal conditions. However, a number of important questions remain open, the most significant of which concerns signal processing. Here we continue our bottom-up analysis by exploring the effects of harmonics processing on the images obtained. Our simulations suggest that there are no imaging artifacts inherent to the filtering process used but that harmonics averaging is not an appropriate method for enhancing subatomic contrast due to variations in the harmonics ratios across the surface. Instead, a promising approach may be the individual mapping of the first two harmonics, which are expected to dominate the contrast under the conditions studied by Hembacher et al.

scholarly journals First-Principles Calculation of Laser Crystal Multiplet Levels via Hybridized Density Functional Theory and Configuration Interaction within the OLCAO Method

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Benjamin Walker
Keyword(s):  
Density Functional Theory ◽  
Configuration Interaction ◽  
First Principles ◽  
Density Functional ◽  
Energy Levels ◽  
Computational Method ◽  
First Principles Calculation ◽  
Functional Theory ◽  
Racah Parameters ◽  
Analytic Computation

Computation of highly-localized multiplet energy levels of transition metal dopants is essential to the design of materials such as laser host crystals. A purely first-principles density functional theory-configuration interaction (DFT-CI) hybrid computational method has been developed to accurately compute multiplet energy levels for single atoms of carbon, nitrogen, oxygen, sodium, aluminum, silicon, titanium, and chromium. The multiplet energy levels have been computed with close experimental agreement in terms of magnitude and degeneracy, and the method does not depend on empirical information (i.e. Racah parameters). The computed multiplet energy level results are distributed according to term symbols, which are then compared to experimentally-observed multiplet energy levels. The hybrid method consists of analytic computation of two-electron integrals via the DFT-based orthogonalized linear combination of atomic orbitals (OLCAO) method, which are subsequently used as input for the CI-based discrete variational multi-electron (DVME) method to obtain the multiplet energy values.Keywords: exchange-correlation; elecron repulsion integral; multiplet; DVME; OLCAO; density functional theory; configuration interaction

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