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Questions tagged [geometry-optimization]

Questions about finding the molecular or material geometry that has the lowest energy.

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27 votes
2 answers
3k views

Is it right to neglect very small imaginary frequencies?

I'm running a DFT optimization (B3LYP/def2-TZVP) and frequencies in ORCA for a molecule. And I get one or two very small (1-6 cm^-1) imaginary frequencies which corresponds to a slight bend of the ...
Roman's user avatar
  • 2,373
16 votes
3 answers
4k views

Geometry optimization for n-layers in VASP

What is the best way to optimize monolayer geometry in VASP? Should the same method be used for an n-layer (n=2,3,4,5)?
M_Fisher's user avatar
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15 votes
3 answers
203 views

Candidate structures for global minimum determination

What are the best packages that can generate candidate structures for quantum chemical optimization (DFT or CCSD) to find the global minimum? I am working on the gas-phase small inorganic clusters (...
Somnath Bhowmick's user avatar
13 votes
1 answer
7k views

When should "vc-relax" be performed over "relax" calculations in Quantum ESPRESSO?

I'm new to Quantum ESPRESSO and I have read that there are several scenarios when relax calculations are preferred over vc-relax calculations, for example in maintaining vacuum while modelling surface....
Anoop A Nair's user avatar
  • 4,506
12 votes
2 answers
303 views

Permissible amount of forces on ions in a relaxed structure

An equilibrium structure would be at a local minimum but that doesn't happen with all relaxation calculations. Relaxed structures tend to have some resultant forces on ions. What amount of these ...
Hitanshu Sachania's user avatar
11 votes
1 answer
275 views

How would one find a material's equilibrium structure at any specific temperature?

Let's take an example of a simple FCC material, a binary alloy. Above absolute zero K, the alloy will start to disorder and become an FCC solid solution. The alloy would develop defects as it ...
Hitanshu Sachania's user avatar
25 votes
3 answers
5k views

Geometry optimization: what happens in the algorithm?

Geometry optimization using density functional theory (DFT) is done by moving the atoms of a molecule to get the most stable structure with the lowest possible ground state energy. My question is what ...
Shalini's user avatar
  • 1,615
14 votes
1 answer
299 views

Is there a software that has implemented forces of TDDFT calculations for solids?

I'd like to investigate the structural relaxations of the excited state for periodic systems. BSE and TDDFT are two promising methods for this purpose. While there is a discussion on forces with BSE ...
Xiaoming Wang's user avatar
14 votes
5 answers
2k views

Are dispersion correction methods for DFT (such as D3) useful for geometry optimization?

For what I know the DFT-D3 method or similar corrections that take into account dispersion effect, add this type of contribution through calculation of atom pairwise interactions at the end of an ...
NickZ's user avatar
  • 1,499
13 votes
1 answer
381 views

Excited state energy gradient during geometry optimization of a target excited state

During the geometry optimization of the ground state of a molecule, we try to optimize the energy gradient with respect to the nuclear positions such that the system remains in its lowest energy state....
Bikash Patra's user avatar
11 votes
2 answers
1k views

Analytic gradient for DLPNO-CCSD

Is there a formula for analytical gradients (for geometry optimization) for the DLPNO-CCSD method? I ask because I know that it is not implemented in ORCA. Maybe PNO-CCSD is implemented in MRCC or ...
Paulie Bao's user avatar
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8 votes
1 answer
621 views

Do the U values affect structure optimization with the DFT+U simulation to optimize crystal structure?

I am trying to do structure optimization of TiO2, since titanium is a transition metal, I need to use DFT+U to simulate the right band structure, but the electronic band structure would also affect ...
Jack's user avatar
  • 2,057
7 votes
3 answers
201 views

What would be the preferred format for a geometry database?

Introduction (analogy to basis set database files) Many programs have a database of basis sets stored in a file such as the following (so that users can just specify in their input file something like ...
Nike Dattani - No Free Time's user avatar
7 votes
1 answer
127 views

How many non-redundant internal coordinates are needed for optimisation of linear molecule?

I have been working to implement optimisation in internal coordinates (for a transition state search software I am working on). However, the implementation details are almost always glossed over in ...
S R Maiti's user avatar
  • 7,021
6 votes
1 answer
971 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
  • 61
3 votes
1 answer
65 views

ASE GPAW variable cell relaxation

Ive been trying to do a vc relax using GPAW and ASE on the BaTiO3 unitcell. The input file is as below: ...
Atom's user avatar
  • 1,005
3 votes
1 answer
765 views

A different way to optimize triplets?

I am studying a system with TD-DFT method implemented in Gaussian. I am not sure whether this two inputs are adequate by the mean of output - optimization of T1? ...
farmaceut's user avatar
  • 576
2 votes
1 answer
257 views

Optimal choice between ISIF = 3 and ISIF = 4 for lattice parameter and atomic position relaxation in VASP calculations

In my VASP calculations, I am interested in simultaneously optimizing both the lattice parameters and atomic positions of my system. I understand that using ISIF = 3 allows for relaxation of both ...
Jaafar Mehrez's user avatar