Questions tagged [density-functional-theory]

It can be shown that the energy of a given multi-electron quantum state can be expressed as a sum of a term depending only on the external potential and another which is a universal functional of the electron density. Density functional theory is the development and use of these universal functionals to calculate properties of quantum many-body systems.

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Kinetic preconditioning

Publication arXiv:0804.2583 describes a method for doing self-consistent iteration without having to diagonalize the Hamiltonian operator at every step. IX. PRECONDITIONING As already ...
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Density functional theory: Total energies and forces

In DFT, forces are calculated using the Hellman-Feynman theorem, such that: $$\frac{\text{d} E_\lambda}{\text{d} \lambda} = \left \langle \psi_\lambda \left|\frac{\text{d} \hat{H_\lambda}}{\text{d}\...
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Does quantum espresso and VASP use same same self-consistent-field procedure?

The codes Quantum Espresso (QE) and Vienna Ab initio Simulation Package (VASP) both use plane wave basis sets and psuedopotentials. Most of the codes in both implementation of DFT uses Fortran code. ...
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How does density-functional-theory scale with cell size, not with number of electrons

The discussion in How does density functional theory scale with system size? already tells, how DFT scales with the number of electrons. I want to simulate some clusters, so the simulation cell ...
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How to make supercell of partial occupancies for DFT?

In the case of partial occupancies (for example, this CIF), a supercell should be made for DFT calculations. However, numerous supercells can be built from a lattice (in the above example, 200 ...
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Is there a software package for Quantum Monte Carlo estimation of the exchange correlation functional?

Quantum Monte Carlo (QMC) calculations historically have been used to parameterise the exchange-correlation functionals for Density Functional Theory (DFT). For example, this article explains a way to ...
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Crank-Nicolson integrator: oscillations with complex matrix

I'm working on a Real-Time TDDFT implementation and I am currently comparing different propagation schemes for the propagation of the Kohn-Sham wave function, $$ \phi(t+\Delta t) = \hat{\mathcal{U}}\...
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Matrix exponential by eigenvectors - implementation issues

I posted a similar question yesterday but I deleted it since I think that I had to reformulate it after some insights. I want to calculate $$ \exp(-i\Delta t\,\mathcal{H}) = V\,\mathrm{diag}(\{\exp(-...
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Simple open-source Quantum chemistry or DFT code in C/C++

I know lot of density functional packages in fortran, including one which we are developing in our group (Fireball-DFT) but I don't like fortran very much and I would like something which is easier ...
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Gaussian geometry optimisation: molecule is getting dissociated into sub group?

I was trying to optimise CdSe (Cysteine) molecule using a semi-empirical method in Gaussian 09 (and gaussView) for a preliminary study of quantum dots. But it seems as the number of iterations ...
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CPU for ab-initio DFT calculations

I need to build a new desktop PC, where ab-initio DFT calculation going to be performed. I am searching for a CPU in value range 600 - 1000€. I was thinking about six-core Intel Core i7-6850K or 8-...
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Choose of basis set [closed]

I am engaged with the syntheses and DFT calculations of coordination complexes. I wonder how can I set up the basis set for carried out using B3LYP method and mixed basis sets of LanL2DZ for Pd and 6-...
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Quantum Chemical Calculations is there a book for which method to use with what problem?

Does anyone know of a book that will outline which quantum chemical methods are appropriate for what problems? I am trying to make informed choices before I start using computational resources. It is ...
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Ways to start ab initio MD from classical MD

I am running molecular dynamics simulations of water for testing purposes. The box is quite small, if you ask a guy running classical MD, and relatively large, if you ask a DFT guy: I have 58 water ...
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Why is potential energy of dimer in DFT scan at large distance not zero?

I am a newbie in DFT calculations. I did potential energy scans with GAUSSIAN 09 for different dimers, i.e. ...
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Calculation of phonon dispersion

I have a couple of conceptual questions regarding the calculation of phonon dispersions. I wish to calculate the phonon dispersion of Nickel with my lattice vectors given by [111], [1-10] and [11-2] (...
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Code/package for Quasiharmonic approximation

I'm trying to find some finite temperature properties using ab-initio simulations; and for this, I'm looking for a tool to be used as an auxiliary to DFT simulations (in VASP) to implement ...
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Installing GPAW (Python DFT package) on a computing cluster

I'm in the middle of installing GPAW on a cluster but I'm running into problems building the "gpaw-python" interpreter, its job is to allow users to execute parallelised GPAW calculations. Following ...
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Suggest methods and basis sets for a variety of systems [closed]

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable method/...
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Reproducibility in molecular dynamics trajectories

Let's say I have two molecular dynamics (MD) simulators, A and B, which implement the following interface: $$ \left\{\vec{x}_i(t = 0), T_i, t \right\} \rightarrow \left\{\vec{x}_i(t), \vec{F}_i(t) \...
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Does energy decrease with basis set size in density functional theory?

Based on the variational principle, one might expect that the ground state energy of a density functional theory (DFT) calculation will decrease as the basis set size increases. (As I understand it, ...
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How does density functional theory scale with system size?

Theoretically, how does the time to do a density functional theory (DFT) calculation scale with the number of electrons? I'm interested in "typical" DFT implementations such as VASP, ABINIT, etc., not ...
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Implementing simple atom model using density functional theory (DFT)

I am trying to write computer code which will find the energy and density function for a atom with Z protons and N electrons. I am working in 1D for simplicity and would like to make the overall code ...
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What is the difference between ECPs and ADF frozen cores?

As the title suggests, what are the differences between the frozen core approximation as implemented by Amsterdam Density Functional and effective core potentials (ECPs)?
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Limitations of Density Functional Theory as a computational method?

This question arises from the need I have to prepare a lesson on the limitations of Density Functional Theory as a computational approach. I would like to know not only the limitations, but also ...
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Discretization of Classical Density Functional Theory (CDFT) problems

I formulate questions about ion densities in biological and materials problems using Classical Density Functional Theory, as in this paper which is also on the arXiv. The discretization in that paper ...
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Pauli repulsion contribution in electronic structure computations

I am looking for a method to estimate the contribution from Pauli repulsion to the interaction energy of a molecular dimer in an electronic structure computation (e.g. with Density Functional Theory). ...
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How is B3LYP implemented in Gaussin 0*, GAMESS-US, Molpro, … etc?

Specifically I want to extend work involving B3LYP started with Gaussian 03 but continued with GAMESS-US. The energies provided by the default B3LYP methods are not the same. There is a discussion ...