Questions tagged [geometry-optimization]

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

Filter by
Sorted by
Tagged with
3 votes
1 answer
65 views

Failure to converge geometry of ringed structure

Hi I'm trying to optimise a molecule by using the b3lyp/6-31G(d) method , the calculus took more than 2 days and the energy never converged . Here is my input code ...
3 votes
0 answers
35 views

Restart geometry optimization in Gaussian after hangup error

I am trying to optimize the geometry of a paraquat molecule interacting with a gold bulk. The optimization is stopping after a few steps. The error shown in the .log...
5 votes
1 answer
30 views

How to restart an interrupted TS optimization job in Gaussian16 without the CalcFC option from the chk file?

I have to do the TS optimization of a very large structure. Initially, I used the typical opt(ts,calcfc,noeigentest) at the route section, but during the ...
3 votes
0 answers
44 views

Lennard Jones Clusters in Python

I would like to explore the global optimisation of Lennard-Jones clusters in Python. I do not come from a physical chemistry background. I would like to be able to calculate the cluster energy ...
9 votes
3 answers
200 views

Which output file from CASTEP after geometry optimization is like with the CONTCAR from VASP?

I am trying to use the atomic positions in geometry optimized crystal structure to get the radial distribution function. I know that some codes can read the positions of the atoms from the CONTCAR ...
6 votes
1 answer
134 views

Converging geometry of iron slab

I am a sort-of-beginner in Quantum Espresso. I do understand certain terminology in the INPUT file but I am faced with a dilemma. I have been trying to optimize $\ce{Fe}(110)$ system of 100 atoms ...
2 votes
0 answers
32 views

How to solve "step out of bounds" error in Gaussian?

I am trying to optimize a molecular geometry with Gaussian 16 and this is the line of instructions: ...
2 votes
0 answers
50 views

CP2K geometry optimization SCF takes 3000s for a step

I am new to CP2K and doing a geometry optimization for a cluster. At the beginning everything looks good, each SCF step takes about 13 seconds, the energy drops quickly and the convergence looks like ...
2 votes
1 answer
78 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? ...
4 votes
1 answer
106 views

Decide the position of oxygen vacancy via the configuration with the lowest energy?

I am trying to determine the position of oxygen vacancy in $\ce{TiO2}$, is it reasonable to decide it by choosing the configuration with the lowest energy? It doesn't feel quite right to always choose ...
7 votes
1 answer
193 views

Molecular geometry optimization for cyclooctatetraene with pyscf

I am trying to reproduce the cyclooctatetraene isometrization process pulished here. In figure 3 of the paper, it shows the potential energy surface as a variable of the polar angle using the CAS(8,8) ...
1 vote
0 answers
134 views

Error: hangup in Gaussian 09

I have the following problem to run a calculation using Gaussian 9. The calculation starts running and after a few hours stop. The nohup file has the following ...
4 votes
1 answer
513 views

Reciprocal lattice and k-lattice belong to different groups in VASP

I am trying to do geometry optimization of TiO2 with VASP. Here is the POSCAR file, which I get from the Materials Project. ...
2 votes
0 answers
81 views

Force convergence in Wannier orbitals based DFT code

I am working on Pt(111) / nanoparticles with various ligands, I am mainly using two softwares: A well known general purpose plane-wave code (Quantum Espresso). A less known software that is also ...
25 votes
2 answers
766 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
1 answer
244 views

What are the output files generated by an NEB calculation?

I just used Orca for the first time. Can someone address me a valid guide to understand all the files in the directory? I'd like to perform a Nudged Elastic Band (NEB) calculation, but I'm stuck ...
5 votes
1 answer
229 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
0 answers
198 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
1 answer
87 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
2 answers
336 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
1 answer
116 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
1 answer
343 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
1 answer
112 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
1 answer
181 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 ...
11 votes
1 answer
176 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 ...
9 votes
1 answer
327 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 ...
6 votes
2 answers
379 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?
11 votes
1 answer
188 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
1 answer
59 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 ...
3 votes
0 answers
189 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 ...
16 votes
1 answer
497 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 (...
6 votes
2 answers
222 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 ...
4 votes
1 answer
100 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
1 answer
47 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 ...
15 votes
2 answers
450 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. ...
6 votes
0 answers
113 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 ...
5 votes
1 answer
104 views

Define a geometry region using 'for' loop in MuMax3

I was trying to define regions using a 'for' loop. Please find the regions: ...
14 votes
5 answers
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?
6 votes
2 answers
486 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
2 answers
369 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
2 answers
97 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. ...
13 votes
1 answer
936 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
0 answers
95 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
1 answer
378 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
5 answers
1k 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 ...
14 votes
1 answer
216 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 ...
6 votes
1 answer
296 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, ...
9 votes
1 answer
185 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=...
8 votes
1 answer
387 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. ...
14 votes
3 answers
2k 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)?