Questions tagged [numerical-convergence]
For questions about numerical convergence in molecular and materials modeling questions.
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DFT warn: LUMO = HOMO
I'm trying to do DFT calculations at gamma point of carbon atoms with periodic boundary conditions and atomic orbital basis using the package pyscf.
I have noticed ...
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energy fluctuations in NVE ensemble in molecular dynamics
One can check if the timestep used in molecular dynamics is small enough by looking at the energy conservation in a NVE simulation. From what I understand, due to errors in the integrator (for the ...
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Converging a Quantum Espresso PW geometry relaxation for a perovskite structure
I have been trying to perform a geometry relaxation of a CsPbI3 perovskite for several weeks now. I know that this structure converges with the same thresholds in CASTEP. I am using the PAW pseudos ...
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Never converging phonon calculation in a supercell (Quantum ESPRESSO)
I'm trying to calculate with Quantum ESPRESSO the phonons at the Gamma Point of a Supercell of rutile. I have generated the supercell itself with VESTA and I have tested the convergence for a 2x2x2 k-...
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Convergence Issues in VASP Relaxation Calculations
I'm encountering convergence issues in my VASP relaxation calculations, specifically related to the message 'BRIONS problems: POTIM should be increased.' I've tried adjusting POTIM, but I'm still ...
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Error in 2D Ewald sum for a multipolar expansion
I am attempting to calculate the potential of a particle at the center of an infinite two-dimensional lattice as per the following reference:
Reference: Lambin, PH & Senet, P. Ewald Summation of ...
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convergence not achieved after 80 iterations [closed]
I am trying to run a scf calculations to obtain the band structure. However, in the output file, it is show that the convergence is not achieved after 80 iterations.
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VASP: Meaning of Certain Output Tags
This is just a quick question about the output tags in VASP. My output file is of the form:
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LBFGS -- Incomplete Convergence due to BadIntpln [closed]
I am doing energy minimization of a molecular system in TINKER. While doing so, I am getting the error in the title of this question. What might be my problem?
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Can the the relaxed energy of a material system (eV/atom) computed by DFT using VASP be positive?
If it is positive, why is it so? Is it due to specific convergence criteria or choice of pseudopotentials? I cannot check the convergence of the DFT calculations as they have been downloaded from a ...
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What should be the criteria of convergence over ENCUT?
For example, should a computation be considered to converge when the differences in energy per atom are smaller than a certain value?
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Convergence issues in DFTB+ calculations?
I am trying to calculate the Fermi level of a DNA-graphene system. I was able to get the calculations for graphene and DNA strand to converge separately. However, when I try to calculate the same for ...
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Dirac exchange energy and X_alpha LDA methods
I want to make a DFT code (by myself) that works in the RKS LDA H2 configuration. This post is a continuation of here.
Now by adding the Vosko, Wilk, Nusair correlation I have much better results :
...
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6
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1
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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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Total number of electrons from DOS and PDOS - what's the theory behind it?
Let say we need to determine the total number of electrons of an FCC material (let say, two silicon atoms in the unit cell, using numerical/mathematical approach.
How can we get the total number of ...
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Electronic Convergence Issues with Nonlocal vdW-DF Functionals (in VASP)
Compared to say the DFT-D3 type of dispersion corrections (set with IVDW in VASP), I've found the nonlocal vdW-DF functionals (described here in the VASP Wiki) to be much more difficult to converge ...
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How does charge mixing work?
When doing DFT calculations on certain magnetic materials, convergence can be difficult. This problem can be solved by changing the mixing parameters (e.g. AMIN and BMIX in the INCAR file of VASP). My ...
user5405
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What are the limitations of FCI?
I am aware of the fact that Full Configuration Interaction scales poorly. Taking into account that the number of $n$-times excited Slater determinants of an $N$-particle System with $M$ basis ...
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How to perform a DFT/def2-PPCBS extrapolation on NWChem [closed]
I'm planning to analyse an extremely complex molecule on NWChem(it's practically the only free computational package available package here, and the molecule is so large that running a seemingly ...
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The relationship between average eigenvalue and convergence performance in VASP?
I meet some convergence problems when doing self-consistent field calculation in VASP, I find some parameters on VASP wiki that might be able to tune the convergence performance. But I don't quite ...
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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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Use of higher-order integrators in molecular dynamics?
The usual verlet integration scheme for propagating molecular dynamics according to Newton's equations of motion looks like the following:
$$
x(t+\Delta t)=2x(t)-x(t-\Delta t)+a(t)\Delta t^2
$$
This ...
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What are the advantages of the Davidson diagonalization method over other sparse matrix diagonalization methods?
I am interested to understand the advantages of the Davidson diagonalization method over other sparse matrix diagonalization routines. For instance, Intel MKL.
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How to make SCF converge in SIESTA?
I am trying to optimize some 4 atom Ni clusters. There are 4 types: one linear, one zigzag, one 2D and one 3D.
Using the setup below, I don't get the calculations to converge even after 1000 SCF steps ...
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DFT Vasp calculation not converging when doing a SCF calculation for monolayer MoS2 [closed]
I am trying to calculate the electronic structure of Monolayer Molybdenum Disulfide ($\ce{MoS_2}$) using Vasp. However, I encounter problems with convergence. It does not seem that my calculations ...
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SCF Calculation not converging after two decimal places in Quantum ESPRESSO
I have been trying to do geometrical optimization for ZnSe Quantum Dots using Quantum ESPRESSO.
The convergence is very slow, so slow that even after 200 iterations I could not get convergence. I ...
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Why does the VASP electronic step not stop after getting converged?
I have just implemented VASP code with Gamma K-point, POSCAR of 128-atom supercell and INCAR like this:
...
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Is it possible to get complex numbers as solutions for a secular determinant in simple Hückel method (SHM)?
Past semester we revisited the Hückel molecular orbital theory at class. One day I was trying to solve some problems with SymPy, a Python module that is a computer algebra system (CAS), and noticed ...
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DFT Knowledge Check for Posed Problem
Currently I am trying to apply to a graduate program overseas. They require me to include a research proposal in my application. My topic of interest is computational materials science.
So, one ...
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Smearing and charge balance for tungsten with interstitial oxygen in Quantum ESPRESSO
What smearing would be ideal for a bcc W with interstitial O atom. I am running 3x3x3 unit cells with one N interstitial.
I am having convergence issues in relax ...
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Charge density convergence within VASP using spin polarized DFT+U
I am noticing a possible convergence problem in a magnetic $U$ system I am studying. In the OSZICAR file I often see the rms(c) value go to about ...
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Are there examples of ab initio predictions on small molecules without the "major approximations"?
In most textbooks the precise Schrödinger euqation of a molecule is given (and the "beautiful thing" stops here), then born oppenheimer approximation is made, then layers of other ...
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Failure of CP2K density functional software to converge for a 64 Si atom amorphous structure
The structure was created using Stillinger Weber with LAMMPS.
The command I used was the following:
...
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Are there any other options beyond increasing the k-sampling and the number of unoccupied bands, to achieve better results?
I am trying to determine the optical properties of bulk Aluminium and related alloys using Quantum ESPRESSO. I am using both the epsilon.x and the simple.x modules to get wavelength-dependent ...
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adaptive k-mesh
Are there any known codes or scripts to generate an adaptive k-mesh for DFT calculations? For example, I'd like to make the k-mesh near the $\Gamma$ point (e.g., half the zone) more denser ($20\...
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Input constraints while comparing different DFT calculated properties for the same material but different atomic arrangement
Let's consider a fictitious AB type binary alloy. AB is known to exist in a B2 type ordered ...
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k-points convergence for spin polarised vs non-polarised DFT calculations
Spin-polarised calculations come at a computational cost and I tend to take ISPIN = 2 only after I'm done with a proper initial relaxation of the structure, so the ...
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ASE's fmax and FHI-AIMS's relax_geometry bfgs "tolerance". Are they same? [closed]
They look like the same thing, but their definitions are confusing. Additionally, while it's possible to use 'tolerance'< 0.05 in AIMS easily, in ASE, some structures never optimize if you choose ...
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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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Calculating diffusion coefficient from Mean Squared Displacement
I am performing a molecular dynamics simulation and I have calculated the velocity autocorrelation function (VACF), $\psi (t)$ and mean square displacement, $\langle (\Delta r)^2 \rangle$. In my ...
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How big should a supercell be in phonon calculations?
Is 2x2x2 enough, or is larger needed? I know that a convergence test must be carried out, but increasing supercell size enormously increases computational time, and I am using the Python program ...
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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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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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How should one choose the time step in a molecular dynamics integration?
Choosing too small of a timestep leads to an unrealistic simulation time, whereas too big of a timestep leads to the system not being represented correctly (or, in the case of an algorithm like SHAKE, ...
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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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