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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At what point in the Hartree-Fock formalism is the Fock operator introduced?

I seem to be having a conceptual problem with HF theory as to where the Fock operator comes from. In order to explain the context of my conceptual problem, I will include how HF was derived according ...
Kevin Freddo's user avatar
6 votes
2 answers
145 views

How do I get the energy, if I have the wavefunction?

I recently wrote a simple HF SCF program for my understanding and realized that I do not fully understand such QM calculations. Suppose I have the ground state gaussian wave function of a system, $$ \...
ipcamit's user avatar
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Discrepancy between Force Convergence in Geometrical Optimization and SCF Calculation in VASP: Reasons and Troubleshooting Suggestions

During a geometrical optimization of ions and lattice parameters in VASP, the forces acting on atoms were minimized to less than 0.01 eV/Å. However, when performing the subsequent self-consistent ...
Jaafar Mehrez's user avatar
5 votes
1 answer
255 views

SCF calculations for new materials with unknown properties (e.g. charge, spin, magnetization) using Quantum Espresso

Performing SCF calculations for crystal structures using Quantum Espresso sometimes gives me this error. ...
Prashant Govindarajan's user avatar
4 votes
0 answers
290 views

Interpretation of total energy in SCF calculation using Quantum Espresso [closed]

I am performing SCF calculations using Quantum Espresso for crystalline materials to determine the band gaps and energies. A sample output for one of the crystals is shown below. ...
Prashant Govindarajan's user avatar
2 votes
0 answers
49 views

How can I correctly create the input files for DOS and Optical Properties of a supercell using Quantum ESPRESSO? [closed]

I have a unit cell, and I want to create a 3x3x3 supercell. Please, I need guidance on how to create properly the input files for Density of States (DOS) calculation (SCF and NSCF) and the input files ...
Camilla's user avatar
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3 votes
1 answer
288 views

Advice on converging a restricted open-shell DFT (rob3lyp/LANL2DZ) single point Gaussian09 calculation for a triplet spin-state molecule?

I am running a single point calculation on a fragment of a molecule using restricted open-shell theory. The fragment is in the triplet spin-state and of pentagonal planar structure (D5h). I ran the ...
Kevin Freddo's user avatar
5 votes
1 answer
77 views

Using Hindered Rotor Scans With Different Convergence Criteria from Gaussian

I am having trouble with a difficult convergence in Gaussian16. I am running two separate PES scans for hindered rotors in my molecule that will eventually be used in subsequent rate calculations. I ...
user avatar
3 votes
1 answer
143 views

Why do we specifically need an SCF-generated charge density for calculating the density of states (DOS) and band structure?

Why do we specifically need an SCF-generated charge density for calculating the density of states (DOS) and band structure?
Trivaani Yadav's user avatar
6 votes
1 answer
428 views

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 ...
ipcamit's user avatar
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5 votes
1 answer
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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 ...
Everson Gomes's user avatar
5 votes
1 answer
335 views

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 ...
lela2011's user avatar
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2 votes
0 answers
469 views

How to read two electron integrals from pyscf [closed]

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 ...
lela2011's user avatar
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19 votes
4 answers
2k views

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
778 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 ...
Jack's user avatar
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5 votes
1 answer
330 views

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. ...
Camps's user avatar
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6 votes
1 answer
909 views

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 ...
Kevin's user avatar
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6 votes
1 answer
506 views

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 ...
147875's user avatar
  • 663
6 votes
2 answers
578 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 ...
user avatar
6 votes
1 answer
54 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},...
Wychh's user avatar
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12 votes
2 answers
861 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 ...
Wychh's user avatar
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8 votes
1 answer
542 views

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 ...
PHy's user avatar
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8 votes
1 answer
1k 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 ...
ismail benaicha's user avatar
8 votes
1 answer
820 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 ...
UJM's user avatar
  • 2,601
10 votes
3 answers
389 views

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} ...
Firman's user avatar
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13 votes
0 answers
144 views

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. ...
Andrew Rosen's user avatar
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10 votes
1 answer
494 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 ...
ismail benaicha's user avatar
9 votes
1 answer
544 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. ...
Atom's user avatar
  • 1,015
17 votes
3 answers
890 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 ...
S R Maiti's user avatar
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13 votes
2 answers
1k 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 ...
UJM's user avatar
  • 2,601
18 votes
2 answers
9k 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'?
Ashique Lal's user avatar
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9 votes
0 answers
170 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 ...
Bo Peng's user avatar
  • 675
12 votes
2 answers
2k 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 ...
UJM's user avatar
  • 2,601
9 votes
2 answers
474 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): ...
Wychh's user avatar
  • 2,157
16 votes
1 answer
676 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 ...
Thomas's user avatar
  • 9,092
20 votes
5 answers
1k 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 ...
Nike Dattani - No Free Time's user avatar
19 votes
3 answers
414 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?...
Nike Dattani - No Free Time's user avatar
12 votes
2 answers
1k 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: ...
Wychh's user avatar
  • 2,157
11 votes
2 answers
187 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 ...
Dmitry Eremin's user avatar
12 votes
2 answers
622 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)...
ipcamit's user avatar
  • 545
12 votes
2 answers
271 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 ...
Paulie Bao's user avatar
  • 3,953
18 votes
2 answers
1k 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 ...
sonia rani's user avatar
9 votes
4 answers
524 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, ...
Eugene Chybisov's user avatar
15 votes
2 answers
614 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 ...
Tyberius's user avatar
  • 15.5k
23 votes
4 answers
2k 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 ...
Michael F. Herbst's user avatar