Questions tagged [self-consistent-field]
For questions related to performing calculation using the self consistent field (SCF) algorithm, for example Hartree-Fock and Kohn-Sham Density Functional Theory.
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SCF energy keeps on fluctuating between two values, instead of converging, why?
Sometimes I have observed this phenomenon where my calculations' SCF iterations keep on fluctuating between two values, and not converging. I have observed it in all sort of systems, ranging from ...
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What does "The calculation has reached convergence" mean in Quantum ESPRESSO?
I am a beginner in QE and I have a question. During I was reading about Output file, I saw a part where have it:
"The calculation goes on step by step until convergence is reached. Then we show ...
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Hartree Fock Algorithm too high values for Molecules
I am working on a high school graduation paper on Hartree Fock and have gotten pretty far already. With help from this community, I managed to generate all the necessary integrals and implement the ...
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0
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How to read two electron integrals from pyscf
This is a follow-up question to this one I asked a few days ago. I in the meantime talked to my teacher and generate all the necessary integrals in PySCF. For the one electron integrals that isn't an ...
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4
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What are the physical reasons if the SCF doesn't converge?
I've been mostly using ab initio methods as a routine calculation tool, so even though I know some things from the theoretical side, I still have mostly hands-on experience. One of the things that I ...
user4626
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2
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Does SCF calculation have to be done before calculating DOS?
The standard procedure to calculate DOS or band structure is:
Structure optimization,
SCF calculation,
non-SCF calculation.
According to the vasp wiki, it is because:
Mind: Since the charge density ...
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5
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1
answer
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Which is the recommended way to optimize "big" systems?
Let suppose the we have a "big" system. By "big" I mean a system that have a certain number of atoms that the software is not capable to treat with the default initial parameters.
...
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How does electronic iteration work in a VASP relaxation calculation?
I am a beginner using VASP to do material modeling, and I'm confused about the following questions:
How does the electronic iteration work in VASP relaxation calculation?
Is the electronic iteration ...
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1
answer
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Total Energy vs Energy Cut Off convergence
Why is my plot of 'Total Energy vs Energy cut off' is jagged. Previously ecutwfc was kept at 40, 60 and now 80. But still I am unable to figure why isn't it converging. Where as 'Total Energy vs K ...
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6
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2
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SCF not converging during RHF/STO-3G geometry optimisation
I'm new in the field of QM methods and I've run into a problem for which I can't find a solution online.
I have tried with different basis sets, I've raised the maximum number of iterations and number ...
user115080
6
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1
answer
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Multi-configurational self-consistent field coefficients
The total wave function of $H_2$ can be written as a linear combination of configurations built from bonding and anti-bonding orbitals:
$${\displaystyle \Psi _{\text{MC}}=C_{1}\Phi _{1}+C_{2}\Phi _{2},...
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For DFT and Hartree-Fock, how can we know that we have a true minimum? Is there an equivalent to the "frequency analysis" for geometry optimization?
In a geometry optimisation, one can check if they have reached a minimum by checking the phonons. And to a certain extent, the global minimum can be confirmed by relaxing from different starting ...
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7
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1
answer
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Calculating the band structure of Bi2Se3 with spin-orbit coupling
I would like to simulate $\ce{Bi_2Se_3}$ using a DFT calculation on VASP. However, it seems I am not able to get a result; the electronic steps take $\sim \infty$ of time to complete. Here are the ...
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How To calculate formation energy of Ni doped ZnO system in Quantum ESPRESSO?
I have successfully completed the SCF of doped system Ni doped ZnO using GGA+U. I have checked the SCF.out file and found the energy value : E= -6112.0389 Ry.
Hwo to calculate the formation energy of ...
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Can I run an nscf calculation in Quantum ESPRESSO with disk_io='none'?
I had run an SCF calculation on a crystal system in Quantum ESPRESSO and had collected the converged charge density. However, during the NSCF calculation, there is the generation of ...
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3
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Electronic structure calculations without SCF?
Is there an ab-initio calculation of electronic structure that does not involve self-consistent iteration?
What I mean by self-consistent iteration is the iteration to solve the equation
$$
\mathbf{y} ...
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Handling multiple self-consistent solutions with DFT+U
It is well-established that within the DFT+U framework, one can achieve several self-consistent solutions with greatly varying energies for the same exact magnetic ordering. In 2010, Meredig et al. ...
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How to make sure that my SCF calculation is correct?
hope you are doing well.
I am trying to study the electronic properties of ZnO doped with transition metals (Co, Ni, Fe) using DFT calculation, I am a beginner on DFT calculation using quantum ...
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1
answer
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Should I use a lower threshold for calculations involving SOC?
I'm studying a compound $\ce{VSe_2}$ using the DFT package Quantum ESPRESSO (QE). The following is the input file.
...
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17
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3
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How is "basis set projection" done?
I recently came across something called the basis set projection in Q-chem's manual. What it seems to do is to take the converged SCF in a smaller basis set, and then "projects" that onto a ...
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2
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Getting different total magnetic moment in 'scf' and 'vc-relax' calculations in Quantum ESPRESSO
I am performing a spin polarized DFT calculations in Quantum Espresso on a Co2MnSi ferromagnetic crystal. For this I have performed these steps:
1) Performed ...
- 2,481
17
votes
2
answers
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What is nscf calculation in Quantum ESPRESSO?
I have been using 'nscf' for DOS calculation since it is faster and therefore possible to use a higher kpoints. But why is it faster? why not use it in the place of 'scf'?
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How to do a Delta SCF calculation using ABINIT? [closed]
I am trying to optimize the crystal structure based on Delta SCF. But I am not so familiar with ABINIT at all. As the ABINIT website do not provide further information. It would be super nice if ...
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How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?
I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
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Normalization constant and Roothaan Equations
Roothaan Hall Equations:
The Hartree-Fock equations are a set of modified Schrodinger equations:
$f_{i}\psi_{m}=\epsilon_{m}\psi_{m}$
where:
The Fock operator ($f_{i}$) is given by (restricted case):
...
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15
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1
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Standard values for level of convergence
In matter modelling we use self consistent approaches for calculating different properties. Many DFT codes find the ground state of the system by determining total energy self consistently. Going ...
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18
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5
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What are the types of SCF?
Many of us know the most common types of SCF
(though we can do better than Wikipedia at explaining them):
RHF (Restricted Hartree-Fock), RKS (Restricted Kohn-Sham) [link to answer]
UHF (Unrestricted ...
- 30.8k
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What are the types of MCSCF?
Similar to:
What are the types of SCF?
What are the types of Quantum Monte Carlo?
What are the types of ab initio Molecular Dynamics?
What are the types of pseudopotentials?
What are the types of DFT?...
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What do the rows and columns of a Fock matrix represent?
I am using the pyscf code, where the Fock matrix can be obtained by:
...
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Which SCF energy to use to plot PES after calculations with SMD?
I have a series of molecules calculated (DFT PBE0-D3/def2-TZVP performed in Q-Chem) and I'm ready to plot PES (Potential Energy Surface). I had to increase the grid to get rid of small imaginary ...
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12
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One-center two-electron integrals between 1s STO
As per @user1271772 's suggestion I am asking this question here again.
I am trying to understand SCF cycle by trying to code up solved example from Quantum Chemistry by Levine (page 443, 5th edition)...
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2
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What is the mathematical condition that ensure that the self-consistent field (SCF) procedure must converge?
We know that there is convergence issue of DFT method on study real molecular system. It would be conducive if people could pre-determine if the SCF procedure is converge analytically before starting ...
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How does the Hartree-Fock method improve on Hartree after considering the wavefunction that takes the anti-symmetry property into account?
I am not able to understand the math of this.
After taking the Slater determinant as a wavefunction in Hartree-Fock, does the procedure to find wavefunctions remain the same as in the Hartree method ...
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418
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What programs can do electron integrals and SCF calculations with more than one CPU?
Similar to this question which asks for each answer to provide one software that can do CASSCF: I am interested in software that can do integrals, SCF (Hartree-Fock), and the integral transformation, ...
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Convergence by energy and/or density?
The SCF is an iterative procedure to produce the ground state energy and wavefunction for Hartree-Fock, MCSCF, and DFT. Due to the iteration, one needs to establish convergence criteria. Depending on ...
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Difficult cases for converging Kohn-Sham SCF calculations
In a recent article by Woods et. al.[1] a couple of methods for converging ground-state Kohn-Sham DFT calculations are reviewed and compared. In their test suite they give plenty of examples for badly ...
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