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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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 ...
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7 votes
2 answers
209 views

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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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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6 votes
1 answer
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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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6 votes
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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  • 633
5 votes
2 answers
184 views

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 ...
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6 votes
1 answer
47 views

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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12 votes
2 answers
409 views

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 votes
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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  • 111
8 votes
1 answer
360 views

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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8 votes
1 answer
299 views

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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10 votes
3 answers
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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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10 votes
0 answers
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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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10 votes
1 answer
310 views

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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9 votes
1 answer
137 views

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 votes
3 answers
437 views

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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12 votes
2 answers
561 views

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 ...
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17 votes
2 answers
3k views

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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9 votes
0 answers
108 views

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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9 votes
2 answers
1k views

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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9 votes
2 answers
296 views

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 votes
1 answer
253 views

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 votes
5 answers
695 views

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 ...
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17 votes
3 answers
236 views

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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12 votes
2 answers
747 views

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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11 votes
2 answers
130 views

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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11 votes
2 answers
315 views

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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  • 295
12 votes
2 answers
182 views

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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15 votes
2 answers
550 views

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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9 votes
4 answers
315 views

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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14 votes
2 answers
244 views

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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21 votes
4 answers
1k views

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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