Questions tagged [geometry-optimization]
Questions about finding the molecular or material geometry that has the lowest energy.
56
questions
5
votes
1answer
146 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 ...
5
votes
0answers
44 views
Quantum Espresso error: "SCF correction compared to forces is large: reduce conv_thr to get better values". How to solve? [closed]
I'm getting an error when trying to perform a relax calculation for $\ce{H2}$ on $221$ $\ce{MoS2}$.
I have tried changing conv_thr and ...
7
votes
1answer
72 views
Symmetry group of p-benzoquinone
I am trying to calculate the UV-visible spectrum of p-benzoquinone. In the literature, the point group of p-benzoquinone is $D_{2h}$, but when I optimize this molecule in the ground state with ...
9
votes
2answers
238 views
Is it reasonable to calculate TDDFT excitation energies at a geometry optimized with a different method?
I am working on a project where I have to calculate the TDDFT excitation energies of organic molecules (to compare to the experimental UV/visible i.e. optical absorption spectrum). Now, if I ...
5
votes
1answer
101 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.
...
6
votes
1answer
132 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 ...
5
votes
1answer
101 views
Software for generating ensembles of dimer pairs of organic molecules
For two organic molecules of essentially unlimited size (up to and including, and sometimes exceeding MW = 1000 g/mol), I would like to generate all possible dimer pairs in vacuum. The pairs may be ...
9
votes
1answer
129 views
Geometry optimization using DFT
I have been attempting to optimize the structure of a Si nanowire using SIESTA. The original structure fed into the optimization is as follows.
Once it is optimized, the structure would change to ...
7
votes
2answers
294 views
Geometry optimization with Moller-Plesset MP4
Can we optimize a molecular structure using Moller-Plesset MP4 method on GAUSSIAN software? If yes what keyword do we have to add?
9
votes
1answer
108 views
How to eliminate imaginary frequencies during a Gaussian geometry optimization?
When conducting a minimization on Gaussian software, What are the procedures used to eliminate imaginary frequencies if we have already found a stationary point? Are there any keywords that would help ...
3
votes
0answers
63 views
Simple Pt111 slab not converging using Quantum Espresso [closed]
I would like to perform a "vc-relax" calculation on a simple 3x4x5 $\ce{Pt}111$ slab, this calculation is running well but as soon as I add the ESM ...
5
votes
1answer
56 views
Variable Cell Optimization of Halfnium Crystal
Reference: Density Functional Theory: A Practical Introduction, David Sholl, Janice A. Steckel, Chapter 2, Page No. 46
Hf is experimentally observed to be an hcp metal with c/a 1.58. Perform ...
11
votes
1answer
156 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 ...
5
votes
2answers
168 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 ...
3
votes
1answer
77 views
How to do a proper relaxation of the multicomponent structure?
I have a beta Ti (Space Group 229) structure with 16 atoms, I prepared 15 disordered TiNb structures with 5 atoms of Nb. I did it using VASPKIT. However, before the ...
2
votes
1answer
44 views
Determining the geometry of UOx and WOx for (x=1-3)
Is there a way to work out the geometries for the $\ce{UO_x}$ and $\ce{WO_x}$ species for ($x=1-3$).
I know that deducing the multiplicity (the number of unpaired electrons) in d and f block ...
6
votes
0answers
71 views
How to calculate energy gradient and Hessian with respect to only a few internal coordinates using Gaussian? [closed]
I would like to form the (numerical) gradient and the Hessian of the total electronic energy with respect only to a few internal coordinates (namely, the six intermolecular coordinates of a weakly ...
15
votes
2answers
305 views
What's the best quantum chemistry output parser for the command line?
This question is about tools like Open Babel. Are there any good command-line parsers for quantum chemistry program outputs? A good Python library could come in as a close second.
I am interested e.g. ...
5
votes
1answer
67 views
Define a geometry region using 'for' loop in MuMax3
I was trying to define regions using a 'for' loop.
Please find the regions:
...
6
votes
2answers
453 views
Analytic Hessian at the level of full CI?
This is a follow-up question to my previous question: Computing analytic derivatives of molecular Hamiltonians obtained from solving Hartree-Fock equations.
After looking at various quantum chemistry ...
9
votes
2answers
119 views
Is it possible to do a Gaussian redundant scan with some fixed bonds?
I'm trying to do a redundant PES scan of a hydrogen abstraction in a Gaussian job while maintaining the rest of the system fixed. I need to scan the coordinate where H5 approaches to H6, maintaining ...
5
votes
2answers
82 views
How to use fractional numbers as arguments for keywords in Gaussian input?
I have used both Gaussian09 and Gaussian16 and one thing that seemed unusual to me is that I was unable to enter any fractional number as one of the arguments for a keyword in the Gaussian input file.
...
11
votes
1answer
279 views
Why does Gaussian ignore the opt=maxcycles keyword for optimizations?
I have been using both Gaussian09 and Gaussian16 recently to optimize some metal complexes. The Gaussian manual (for both versions) indicates that the maximum number of steps in a geometry ...
6
votes
0answers
85 views
How to optimize the geometry of beta PHB in VASP? [closed]
I would like to calculate the elastic constants of beta PHB. From this paper. I know that it has P3221 space group. The beta PHB has upward and downward chains, which exist at one lattice site with 50%...
11
votes
1answer
316 views
Choice of coordinate system for geometry optimization
For geometry optimization, most QM codes tend to use internal coordinates. Most codes also support Cartesian coordinates. I have always heard the usual "use Cartesian as a last resort, always use ...
14
votes
5answers
778 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 ...
6
votes
1answer
135 views
Gaussian: Transition state convergence question
I am running a TS computation in Gaussian 16. It performs several steps.
At the end of each there is a summary on whether Maximum Force, ...
23
votes
3answers
1k 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 ...
9
votes
1answer
160 views
SCAN-RVV10 geometry optimization
I'm using SCAN-RVV10 to optimize the hexagonal-BN but the optimized geometry doesn't look true as the calculated interlayer distance is far smaller than the experimental value(exp=3.35 Aangstrom, calc=...
11
votes
1answer
162 views
Using "soft" constraints / bias in geometry optimization?
I study molecules weakly bound to nanoclusters and surfaces.
During geometry optimization, I often run into problems like for example a small metal cluster behave nicely and has a given, stable ...
8
votes
1answer
138 views
What are the input parameters of VASP for 2D material geometry optimization?
Apparently, my input parameters are not good for geometry relaxation of 2D materials using VASP.
...
6
votes
2answers
108 views
Symmetry-preserving low-level structural relaxation
I would like some suggestions on how to do structural relaxation (while I'm at it, let me list some synonyms for search exposure - geometry optimization, structural refinement, energy minimization etc)...
12
votes
1answer
90 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....
10
votes
1answer
130 views
Can I do a "constrained" geometry optimization in Quantum ESPRESSO, such that certain dopants appear in certain positions even after relaxation?
I am studying the magnetic properties of bulk ZnO, so I am doping it with transition metal elements in order to observe the magnetic spectrum. I replace a Zn atom with a transition metal element at ...
5
votes
1answer
101 views
Dispersion correction and band structure
Let's say I optimized geometry with PBE+D3. I want to carry out band structure calculation with HSE06, should I add the dispersion correction to the band structure calculation or not?
I tried both and ...
6
votes
1answer
87 views
Understanding QuantumEspresso Toolbox through Maestro
Anyone here uses Quantum Espresso through Maestro can tell me a bit more about the calculation panel setting:
I understand that -npools option must be divisible by ...
15
votes
1answer
305 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 ...
7
votes
1answer
50 views
Relax vs VC-Relax for interstitial incorporation energy
In order to model an interstitial trapped in a metal lattice, and the associated incorporation energy, which should be used - "relax" or "vc-relax"? I want to understand the ...
16
votes
1answer
428 views
Why is CPHF/CPKS necessary for calculating second derivatives?
This question is coming from an answer to one of my previous questions. During optimizations, QM programs usually compute the gradient(first derivative) analytically, and take a guess of the hessian (...
12
votes
1answer
216 views
Geometric optimization taking a long time. Are my convergence criteria too tight in CP2K?
I have been having trouble with the VIBRATIONAL_ANALYSIS routine. Namely, the routine keeps timing out. I am trying to find the vibrational modes of Pyridine in a non periodic system, as well as $\ce{...
10
votes
1answer
81 views
How to define a nonconventional geometry to obtain exchange spring hysteresis loop structure using MuMax3?
I have tried to simulate the hysteresis loop for the exchange spring structure using Mumax3. I have already simulated the hysteresis loop for the conventional bilayer soft-hard structure. Please find ...
12
votes
2answers
266 views
Comparing calculations in plane wave and atomic orbital bases for the same functional
Let's say I have two codes. One is plane wave, and the other is using atomic orbitals as basis sets. How can I compare these two codes with the same functional? And let's say I want to optimise the ...
6
votes
2answers
142 views
How can I increase the default maximum limit on step size for convergence in quantum ESPRESSO?
When trying to manually optimise the geometry of the crystal, I've faced an issue wherein the code stopped the convergence process after just 100 steps (which was the default maximum). Is there a way ...
10
votes
2answers
383 views
Should I do vc-relax with nspin=2 in Quantum Espresso for magnetic samples?
I'm a beginner when it comes to DFT and Quantum Espresso.
Consider I have a lattice which has associated magnetic properties. So for geometric optimization should I take into account the magnetic ...
11
votes
1answer
2k 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....
11
votes
2answers
453 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 ...
14
votes
1answer
188 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 ...
13
votes
5answers
2k views
Can I use two different codes?
Can I use one code for geometry optimization and another code for a single point calculation on that optimized geometry? Can one publish results like that?
13
votes
3answers
846 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)?
12
votes
2answers
157 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 ...