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9 votes

Convergence testing in DFT calculation

In general, the answer is no. The convergence steps you have taken allow you to obtain electronic structure and electronic energies at your desired precision. Many dispersion corrections (like Grimme'...
Kristof Bal's user avatar
  • 1,341
8 votes
Accepted

Comparing results of various DFT calculations in Quantum ESPRESSO

There are two ways to approach this problem. You can either perform a vc-relax calculation which will optimize/relax the atomic positions as well as the cell ...
Abdul Muhaymin's user avatar
8 votes

Understanding algorithm of Quantum ESPRESSO from scratch

Most plane-wave codes are really very similar, so learning one is learning them all. There are important differences between pseudopotentials, PAW, LAPW, etc, but you can worry about that later.I ...
Tyler Sterling's user avatar
7 votes

At a particular K-point (Monkhorst Pack) grid, SCF calculation is not converging

Yes, if you have fewer k points, there is less to calculate, so one iteration will be faster. However, there is also another effect: if your discretization is poor, the minimization of the energy ...
Susi Lehtola's user avatar
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5 votes

Stopping an ongoing relax calculation with provision to continuing the calculation later on from that checkpoint

How can I interrupt an ongoing relaxation calculation in Quantum ESPRESSO on my system, while ensuring that I can resume it later from the same point? Short answer you can't. Apart from getting the ...
Atom's user avatar
  • 1,015
5 votes
Accepted

what determines the 'Estimated total dynamical RAM ' in a Quantum Espresso calculation

When people talk about the scaling of a conventional DFT implementation being cubic with simulation size, they are talking about the computational time, not the RAM required. The RAM actually scales ...
Phil Hasnip's user avatar
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5 votes
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Non-monotonic behaviour in calculation time with changing 'degauss' value of 'cold' smearing

I summarized our comments above into an answer that you should accept if it answers your question! :) The difference in simulation times is due to more or fewer SCF steps depending on ...
Tyler Sterling's user avatar
4 votes

How to determine energy convergence threshold and force convergence threshold in Quantum Espresso

The parameters etot_conv_thr and forc_conv_thr determine the convergence thresholds for the ionic minimization. When the change ...
manju9's user avatar
  • 176
4 votes
Accepted

Is there a minimum inter-defect distance when introducing point defects into a 2D structure, ensuring defects don't exhibit significant interactions?

It depends on the system and the goal. If the goal is to model truly isolated defects (i.e. not clustered together), then you have to use a system large enough that there are no spurious effects of ...
Tyler Sterling's user avatar
4 votes
Accepted

Is it possible to do a vc-relax calculation using GPAW?

This is more of an ASE question, given that a python script using ASE is employed to set up and run the GPAW calculation. GPAW only is used to compute energies/forces/stresses for a given structure, ...
Kristof Bal's user avatar
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4 votes
Accepted

Why my Relax calculation is not stopping?

I agree that the calculation will likely converge eventually and there is likely nothing fundamentally wrong with the calculation itself. However, this is a defect calculation, and it is worthwhile to ...
Andrey Poletayev's user avatar
3 votes

Can we use Density Functional Theory (DFT) to calculate the second and third-order force constants of a slab?

The third-order force constant tensor is simply a third derivative of the total energy $E$ with respect to all possible combinations of three atomic displacements $\{R_i\}$, i.e. $$\tag{1} \frac{\...
Phil Hasnip's user avatar
  • 7,347
3 votes

What is the Hamiltonian in the adiabatic connection?

I have resolved my problem. The source of my confusion was mistaking the integrand $E_{xc,\lambda}$ at specific values of $\lambda$ with $E_{xc}$ itself. Hybrid functionals can be motivated by linear ...
Hans Wurst's user avatar
3 votes
Accepted

What is the Hamiltonian in the adiabatic connection?

Your $\lambda=0$ definition corresponds to the complete neglect of interelectronic interactions. There is nothing to prevent you from doing that in principle, but the resulting approximation you would ...
Susi Lehtola's user avatar
  • 19.1k
3 votes

Why my Relax calculation is not stopping?

It will stop, hopefully. Since you set a tighter convergence criteria for the forc_conv_thr than the default value, it is just taking more time. If you check the ...
Abdul Muhaymin's user avatar
3 votes
Accepted

vc-relax calculation on two-dimensional slab

Ideally, you would want the x and y cell parameters to change (assuming the 2d material is in the XY plane), whilst the z cell parameter is kept fixed to prevent interaction between the slabs. This ...
Atom's user avatar
  • 1,015
2 votes

Siesta - Segmentation fault error

The error file shows that some library of the name libxpmem.so is missing, and i would guess that it is required for the computation to proceed. This would usually ...
Hemanth Haridas's user avatar
2 votes

Can we use formation/ cohesive energy to express the structural stability of a supercell?

You might want to be more specific about the type of stability you are thinking of. The formation energy would be useful for assessing thermodynamic stability. It sounds as though dynamic and elastic ...
CW Tan's user avatar
  • 1,276
1 vote

Structural stability of Graphene

It was the spin-polarized calculations that led to the issue. In both the isolated carbon atom and graphene calculations, I did not use spin-polarized DFT calculations. However, after reading this ...
Thejan Hasaranga's user avatar
1 vote

Introducing a vacuum space in z direction for 2D monolayer calculations

As your system will be only periodic in 2D, yes, you need to add a vacuum layer (in both sides of your layer) to avoid image interactions. The ideal way to do this is running a convergence test where ...
Camps's user avatar
  • 23.3k
1 vote
Accepted

Identification of all possible H adsorption sites on the surface

A quick search on google scholar returned multiple papers that have used Kinetic Monte Carlo simulations to investigate the binding of small molecules with surfaces. This paper gives the methodology ...
Hemanth Haridas's user avatar

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