Questions tagged [ab-initio-calculations]

For questions about ab-initio (first principle) calculations.

Filter by
Sorted by
Tagged with
4 votes
0 answers
63 views

Is it possible to obtain the current-voltage characteristic for a crystal using the Hartree–Fock (or DFT) calculation?

In continuation of the question of obtaining an electrical conductivity tensor (ECT) from the “first characteristics”, will my following suggestion be correct? Since a crystal with an applied-to-it ...
user avatar
  • 201
11 votes
0 answers
59 views

How to define a chemical bond computationally?

I'm working with an amorphous system. With oxygen, my system has both covalent and ionic bond forming cations. I utilise the Wannier centre approach to define a covalent bond, and my theory is that if ...
user avatar
3 votes
0 answers
66 views

Can the electrical conductivity tensor of a crystal be obtained from a Hartree-Fock calculation?

Let’s assume that a crystal has been calculated by Hartree–Fock (HF) method (or DFT one), i.d., so to speak, the "first characteristics", which are eigenvalues and eigenvectors, as well as ...
user avatar
  • 201
6 votes
1 answer
101 views

Slope of the potential when both molecules "touch"?

My aim is to model the potential energy surface for two colliding H2 molecules. More specifically, I needed the order of magnitude of the slope of the potential at the moment when two colliding H2 ...
user avatar
4 votes
0 answers
80 views

In which part of the Hartree–Fock algorithm (or DFT one) could a neural network be most effectively used?

I understand that the task of implementing machine learning in DFT and Hartree–Fock (HF) algorithm has already been solved, perhaps to some extent, but it is interesting to think about how to ...
user avatar
  • 201
2 votes
0 answers
34 views

How to determine the TA/LA by phonopy

I would like to ask how to use PHONOPY to define which band is LO, TO or ...
user avatar
6 votes
0 answers
72 views

Is there a system of multiple interacting quantum particles for which density can be obtained analytically?

I know that it is impossible for real electrons and nuclei. In the Kohn and Sham approach, a system of interacting electrons is approximated by a system of non-interacting Kohn-Sham particles in an ...
user avatar
4 votes
2 answers
536 views

Which formalism is better suited to model a crystal with defects: Hartree–Fock, Kohn–Sham, or something else?

Let’s suppose that (1) it’s required to calculate a crystal with certain parameters of a crystal lattice; (2) this crystal has some defects (let it be Frenkel defects for simplicity); (3) these ...
user avatar
  • 201
7 votes
0 answers
94 views

How to run 2nd generation CPMD in CP2K?

I believe CP2K by default implements Born–Oppenheimer MD. I have seen many recent papers that use 2nd generation Car–Parrinello MD using CP2K. But I couldn't find any direct way of switching to 2nd-...
user avatar
  • 1,541
6 votes
1 answer
181 views

Raman Spectra in Quantum Espresso

Does anyone have any experience simulating Raman spectra in Quantum ESPRESSO? Following the example 15 that comes with QE, I have attempted to simulate the Raman spectrum of MgO. I know the lraman ...
user avatar
  • 91
5 votes
1 answer
56 views

How are the exponents in a STO-nG basis set obtained?

STO-3G has exponent parameters which can be found in a reference book. Can these parameters be calculated using, for instance, a Hartree–Fock equation for one atom? Or using another way?
user avatar
  • 201
5 votes
2 answers
119 views

ORCA: Dipole moment of LiH from SP calculation

I calculate LiH with ORCA ...
user avatar
  • 357
6 votes
1 answer
105 views

Are there any open source codes that can generate LAMMPS potentials from DFT calculations? [duplicate]

Are there any opensource and freely distributed codes available which can be used to develop classical potentials for LAMMPS? The MEAMfit code is free and opensource, but the input needs to be from ...
user avatar
  • 2,454
5 votes
0 answers
72 views

How to calculate spontaneous polarization of system in VASP

Can anyone describe standard procedure for calculating polarization in VASP. Usually polarization calculation is done on unit cell in VASP or any other codes. For my system with partial occupancies i ...
user avatar
4 votes
0 answers
137 views

VASP error in berry phase calculation, system is not insulated

I am trying to calculate polarization for a system. Vasp is skipping the LCALCPOL tag calculation because the system is not insulated. How can I make the system ...
user avatar
10 votes
1 answer
385 views

How to calculate molecular orbitals of octaoxygen under high pressure?

This question about octaoxygen: Why is octaoxygen diamagnetic?, was asked in chemistry, but I really don't have an answer in terms of molecular orbitals. I think it could be a mixing of the O$_2$'s $\...
user avatar
  • 593
9 votes
3 answers
228 views

The number of orbitals in Gaussian/GAMESS log file

After calculating the energy of a $\ce{CH4}$ molecule with a 6-31G(d,p) basis set, I obtained the Gaussian/GAMESS log file and describe a part of the log file as follows. ...
user avatar
  • 1,335
8 votes
2 answers
659 views

Is there a benchmark paper that takes into account how often each molecule is studied?

There are many benchmark sets in different branches of computational chemistry and physics, that are frequently used to assess the "average error" of a method for a certain property, on a ...
user avatar
  • 6,643
9 votes
1 answer
94 views

How to find the Cauchy stress tensor in solids using ab-initio methods?

I want to find the Cauchy stress tensor in certain materials with ab initio methods. I already have the analytical form of my own definition of "energy" and "forces" (not from DFT),...
user avatar
  • 193
6 votes
1 answer
67 views

Transforming basis functions from Cartesian to speherical

I read the basis set from book A d-type GTO written in terms of the spherical functions has five components (Y2,2, Y2,1, Y2,0, Y2,1, Y2,2),but there appear to be six components in the Cartesian ...
user avatar
  • 69
5 votes
2 answers
185 views

How can I get started on DFT?

This question is simply: How can we use DFT in the field of electrochemistry? What are the best resources (Books, reviews, papers, software ...) to learn about using DFT in electrochemistry? ...
user avatar
  • 1,256
8 votes
1 answer
327 views

What are the electronic steps and ionic steps in VASP?

I am getting confused about what the electronic step and ionic step are in VASP. I used to think that finishing the following loop one time is called an electronic step. but I am not sure how to ...
user avatar
  • 1,601
7 votes
1 answer
168 views

Why does it take 5-10 steps to obtain reasonable orbitals during initialization in VASP?

I am trying to figure out the initialization process of VASP, and I found an INCAR tag NELMDL, on the wiki page of NELMDL, it is said that VASP requires 5-10 steps to obtain the reasonable orbitals. ...
user avatar
  • 1,601
6 votes
0 answers
137 views

How to interpret density of states and band structure of a material? [closed]

I am new on the VASP platform, and have learned how to calculate any material's DOS and Band structure. However, I don't know how to interpret these properties. Can you recommend resources that ...
user avatar
13 votes
1 answer
164 views

Physical interpretation of k-points

What is the Physical interpretation of the k-points used in ab initio calculations? Why must the number of k-points be optimized rather than just using some large fixed number of them?
user avatar
6 votes
2 answers
106 views

Relation between lattice parameter and energy for relaxations

We have been wanting to do relaxation of lattice parameters as a function of the energy. I want to know the mathematical expression for this, and also the theoretical background related to this method....
user avatar
6 votes
1 answer
131 views

Lattice Thermal conductivity calculation error

I have been trying to calculate Lattice Thermal Conductivity on my system using QuantumEspresso. I used phonopy and phono3py. I was successful to run these codes on Si system for practice. Now when I ...
user avatar
7 votes
1 answer
60 views

Comments on the electronic relaxation time variation between nanowire configurations

I am studying Si nanowires with different cross sections. In my work, I plan to evaluate the thermoelectric performance variation between different configurations. To achieve this, my current approach ...
user avatar
  • 2,454
10 votes
1 answer
134 views

Can electron-phonon coupling be extracted from the dielectric function?

Computationally, there are various ways to calculate the electron-phonon coupling constants as a function of phonon index and momentum. My question is about the reverse process. Let us say that an ...
user avatar
  • 303
6 votes
0 answers
51 views

What are Crystal Electric Field Parameters?

What does the following notation mean? $$A_{20}\left<r^2\right> = -100 \mathrm{K}$$ Where $A_{20}$ is termed a Crystal Electric Field Parameter. I often see this notation when reading papers on ...
user avatar
  • 869
7 votes
1 answer
68 views

Changing orientation of SQS structure generated from ATAT

I generated the following SQS cell using ATAT (the sructure is converted to POSCAR format) ...
user avatar
  • 71
7 votes
1 answer
65 views

How Do you Produce your own MEAM Potentials?

I have come across the MEAM Parameter Calibration toolkit (link leads to Wiki, video tutorials, and download link for the package) for fitting your own MEAM potentials [1]. Is this the best software ...
user avatar
  • 869
5 votes
0 answers
48 views

MedeA VASP: Determination of carrier concentration [duplicate]

My question is, how do I calculate the carrier concentration from a DFT study? I am using MedeA VASP for the DFT simulation.
user avatar
5 votes
0 answers
79 views

Methods to study reaction mechanisms in solid state reactions and identifying intermediates [closed]

An example of a solid state reaction: sintering of an initial powder of reactants leading to a product. Densification of the sintered powder giving a highly pure product powder. What methods (ab ...
user avatar
11 votes
0 answers
139 views

How may I calculate the "effective transfer integral" in free electronic-structure software?

I would like to calculate the following four quantities in a free electronic structure program: \begin{alignat}{2}\tag{1} e_1&=\langle\phi_1|H^{KS}|\phi_1\rangle,\\ e_2&=\langle\phi_2|H^{KS}|\...
user avatar
  • 211
12 votes
1 answer
387 views

Comparing GAMESS, OpenMOLCAS and Psi4

Over the years many open-source ab initio packages have been developed and the diversity in subroutines, methods and portability (ability to interface with other software) is quite varied for ...
user avatar
7 votes
3 answers
186 views

How to calculate formation energy using DFT+U?

I noticed that a lot of articles use DFT+U methods to calculate different formation energies when using regular DFT and DFT+U methods. For example, in the attached paper[1] on $\ce{In2O3}$, the ...
user avatar
  • 173
6 votes
0 answers
62 views

Orbital space clustering [closed]

I am interested in how the orbital space of a system can be partitioned into clusters. I read reading 'Cluster many-body expansion: A many-body expansion of the electron correlation energy about a ...
user avatar
  • 1,769
6 votes
0 answers
86 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 ...
user avatar
  • 343
9 votes
0 answers
97 views

Difference of high-frequency and static dielectric constants? [closed]

I found in an article [1] the following definition of FNV (Freysoldt, Neugebauer and Van de Walle) energy correction term for a charged defect in a cubic supercell: $$E_{\text{corr}}=\frac{\alpha_Mq^2}...
user avatar
11 votes
2 answers
427 views

For DFT and Hartree-Fock, how can we know that we have a true minimum? Is there an equivalent to the "frequency analysis" for geometry optimization?

In a geometry optimisation, one can check if they have reached a minimum by checking the phonons. And to a certain extent, the global minimum can be confirmed by relaxing from different starting ...
user avatar
  • 1,769
11 votes
2 answers
259 views

What are the references in multi-reference methods?

After reading What exactly is meant by 'multi-configurational' and 'multireference'? I still don't understand what the multiple "references" are. I understand that you can for example use a ...
user avatar
  • 447
12 votes
2 answers
88 views

What are properties of interest for energy storage materials?

In the field of simulation for energy storage materials, there is always a gap between theoretical calculations and demand for experimentalists. What could be directly calculated from ab initio ...
user avatar
  • 3,599
14 votes
2 answers
190 views

Translating fractional coordinates resulting from conventional cell and primitive cell

I have calculated the band structure of some material where the unit cell was the conventional one (i.e. the lattice vectors are orthogonal). I'm trying now to calculate the same band structure only ...
user avatar
  • 141
7 votes
2 answers
108 views

What quantity to perform CBS extrapolation on for adsorption/binding energies?

When calculating complete basis set extrapolations for quantities, such as adsorption energies or binding energies, which depend on the difference between three quantities (i.e. $E_\textrm{prop} = E_\...
user avatar
  • 348
8 votes
1 answer
330 views

Can I run an nscf calculation in Quantum ESPRESSO with disk_io='none'?

I had run an SCF calculation on a crystal system in Quantum ESPRESSO and had collected the converged charge density. However, during the NSCF calculation, there is the generation of ...
user avatar
  • 2,349
11 votes
6 answers
2k views

How may I calculate the bond length between two atoms?

I have been looking into Lennard-Jones Potential and Morse potential. And what the formulas do is to calculate a potential and the 'well depth' and 'distance at which the intermolecular potential ...
user avatar
  • 544
15 votes
6 answers
2k views

How do I simulate the interaction between two atoms?

I want to build a rough atom interaction simulator, where pushes two (or more) atoms toward each other and they should behave physically correctly: attract, bond or repel with some force. So that is ...
user avatar
  • 544
4 votes
1 answer
63 views

Has there been any work done on fluid dynamic or acoustic modeling of the human oral (or nasal) cavity?

The purpose is for me to develop a deeper understanding of speech production and how distinct features that identify a phenome are produced. ab initio models based on classical & statistical ...
user avatar
20 votes
4 answers
3k views

Solving the Schrödinger equation as a service?

Does anyone know of a company with a cloud-based service which takes some representation of a molecule as an input, and then somehow solves the Schrödinger equation to some level of accuracy and ...
user avatar
  • 371