# Tag Info

18

It depends somewhat on the properties you are interested in. Meaningful vibrational modes, for example, require that your geometry is an energy minimum for the method you are using. Since the experimental structure is unlikely to be energy minimum for an arbitrary electronic structure method, you should optimize starting from the experimental structure. Its ...

16

The question says: I am having trouble understanding the difference between the optimizer options (CG, BFGS, LBFGS). These are three optimization algorithms that evidently are implemented in CP2K for geometry optimization. Maybe the documentation should have said "optimization algorithm" instead of "optimizer", to make this more clear: ...

15

Alot Optimizations are all about finding the minimum in something. Typically in geometry optimization, it is about finding the minimum in energy. At a minimum the derivative of energy with respect to changing position should be zero, or better put, the jacobian should be positive definite. Your question is about bulk systems, however, single molecules are ...

14

Optimizer refers to the algorithm used for finding the minimum of a function. In this specific case the optimizer is referring to "geometry optimization" which seeks to find the local minimum of the potential energy surface. However, optimizers can also be used in other areas in DFT, for example, to optimize the wavefunction. Below I will give a brief ...

13

ForceBalance ForceBalance is one approach which aims at making it easier to create force fields from a combination of theoretical and experimental data. I believe it's within the OpenMM framework. The paper on the work can be found here https://pubs.acs.org/doi/10.1021/jz500737m From the GitHub page it says "The purpose of ForceBalance is to create ...

12

This is a very intriguing question. I'll answer assuming that your CIF is formed by a molecule-based crystal. The structure in such CIF has been obtained usually by the X-ray diffraction technique. With it, you can obtain a single cell that, repeated in the 3 spatial directions, forms the total crystal structure. Considering this, if you isolate just one ...

8

ForceBalance Cody is right, ForceBalance is designed for the task of generating custom force fields. Force fields have a lot of variability in their functional forms, representation of parameters (as text, XML files or objects in code), the possible values or ranges of parameters, the software that runs simulations using the force field, the experimental ...

8

I won't go over what Charlie Crown already described in his answer, but if you don't have experimental data, you can try starting off with the experimental structure of a similar compound that has the same crystal structure (i.e. ZrO2 and HfO2). If there are several options, try them and choose the relaxation that gives you the lowest energy. Just to add a ...

7

This can be readily done using the Atomic Simulation Environment (ASE), if you are comfortable with Python. A tutorial for this exact purpose is described here. Another example using ASE can be found in Section 4.3 of Kitchin's "Modeling materials using density functional theory".

6

The CONTCAR file contains the final position and velocities from a VASP run. You can find out more information from this vasp wiki page or from VASP manual. Please note, the 3rd 4th and 5th lines are the information about lattice constants a,b and c respectively. If you open this in VESTA the values shown for a, b and c are the magnitude of the corresponding ...

6

You can start with this bash script for Aluminum to begin Note: Make sure to fix two quantities while changing third one among INCAR,KPOINTS,POSCAR Lattice optimization for i in seq -w 4.01 0.01 4.05 # change the range needed do cat <<EOF >POSCAR Al bulk FCC $i 0 0.5 0.5 0.5 0 0.5 0.5 0.5 0 1 direct 0.0 0.0 0.0 EOF mkdir$i cp INCAR \$i/ cp ...

2

The question makes no sense, since a solid state system might have different phases, or a molecule might have different conformers. They may all be proper local minima of the energy functional, and with very small overall total energy differences. For instance, J. Phys. Chem. A 117, 2269 (2013) is a benchmark study for the 52 different conformers of the ...

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