Questions tagged [density-functional-theory]
Density functional theory (DFT) is a quantum mechanical model used to estimate the electronic structure of molecules and condensed matter. In broad terms, DFT works by treating all the electrons in the system as a single electron density, and computing physical quantities of interest as functionals of that electron density.
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Free energy at 0 K from density functional theory and statistical mechanics
Helmholtz free energy of a system of atoms (for example — a perfect crystal) at $0$ K can be obtained by performing a static density functional theory (DFT) calculation (neglecting the effects of zero ...
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Curious about entropy and information theory in Bohmian mechanics
I've been playing around with Bohmian mechanics in electronic systems. I really like the interpretation of particle trajectories in terms of the continuity, Hamilton Jacobi equation and guiding ...
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Why do we need two Hamiltonians — the Kohn–Sham Hamiltonian and the second-quantized many-body Hamiltonian — in condensed matter field theory?
Dear members of the condensed matter community, There are two things in the non-relativistic quantum field theory of solids that I cannot quite reconcile: (1) We start from the full crystal ...
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Do one-particle states really exist in solids?
Many theoretical journeys on crystalline matter start their narratives with a completely general description by means of the crystal Hamiltonian \begin{equation} \label{eq: solid-state-hamiltonian} ...
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Computational methods to calculate piezoelectric tensors from Berry phase and phonon approaches [closed]
Recently, I have been exploring methods for computationally calculating piezoelectric properties(tensors), such as Berry phase and phonon-based approaches. I would greatly appreciate any insights into ...
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Approxiamte Atom-wise energy from Hartree-Fock calculation
Is there a way to get atom-wise energies from an ab initio calculation like Hartree-Fock? I will describe some ideas we had and would appreciate any critique, corrections, or alternative suggestions. ...
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Order of Integration for Hartree-Fock Exchange Energy
I am looking at the Exchange energy as an integral over non-interactions greens functions: $$ E_x = - \int \frac{dv}{2\pi} e^{i v \delta'} \int \frac{du}{2\pi} e^{i u \delta} \int d^3 \mathbf{r} \int ...
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Relationship between Wavefunction and Its Energy Derivative in Linearized Augmented Functions
I am studying Richard Martin's book on DFT and in Chapter 17 when discussing linearized methods he first sets up the wavefunction $\psi_l(\epsilon, r)$ giving it a dependence on energy. In linearized ...
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How to break a nodal loop in semimetal?
I have a monolayer semimetal with a nodal loop around Gamma point. The Chern number is 1 because this closed loop. I want to increase the Chern number without additional layer(s). In some papers, I ...
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Permittivity value in density functional theory (DFT)
Density functional theory method requires to solve Poisson equation as given expected charge density. However, it seems that an exact value of permittivity is not required to solve it as if it is ...
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UV-Vis Absorption Spectra of Furan
I did a td-dft for furan using Gaussian 09 to get its absorption spectra. I see the that the largest peak is at 142.55 nm but the excitation energy is shown to be 190.79 nm, at the smaller peak. Is it ...
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What is "fractional coordination number" in grimme-d3 methods? [closed]
Now I am studying Grimme-D3 methods. https://doi.org/10.1063/1.3382344 But I could not exactly understand the "fractional coordination numbers" concept. I think this is not the same idea as ...
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Are all the potentials in the Kohn-Sham equations functionals of $\rho$?
I recently asked this question: Kohn-Sham Equations, but it was rather long, and unfocused. I have now isolated a particular point of confusion. The Kohn-Sham Equations are: $$\begin{equation} \...
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Kohn-Sham Equations
I am trying to understand the Kohn-Sham approach to density functional theory (DFT), and I think I'm really following things, and fall down immediately after we start talking about the fictitious ...
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Why TO phonon frequency is sensible to long-range dipole corrections but LO phonon does not?
I am trying to calculate the phonon dispersion relation in some polar semiconductor materials, including SiC, MgO, and GaN. I found that the frequencies of LO modes in these materials are heavily ...
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