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4
votes
0answers
19 views

Have Finite Difference Time Domain methods made inroads into dynamical simulation of electron and X-ray scattering by crystals?

I'm afraid this question might be too basic or too naive or both, but here goes! For optical diffraction by periodic nano-structures (gratings, semiconductor manufacturing metrology) the rigorous ...
9
votes
2answers
228 views

Is there an energy gap correction factor that needs to be used in DFT calculations?

I am a beginner and have performed the DFT calculation in Quantum ESPRESSO for calculation of the direct and indirect bandgap of Silicon. I found the indirect bandgap to be 0.6551 eV. Now, I have ...
5
votes
0answers
17 views

Is it possible to simulate the Raman spectra via Molecular Dynamics(MD) using the GROMACS package?

I'm new to molecular dynamics and DFT. The aim was to study the Raman spectra of a molecule in a medium. As we know the Raman spectra of a molecule change due to the induced polarization in the ...
10
votes
1answer
248 views

Si energy band values are not matching with literature values

I have performed the DFT calculation for Silicon in Quantum ESPRESO. I have tried to calculate the electronic band structure, the shape of wiggles of bands are mostly matching but the energy values ...
4
votes
0answers
28 views

Is there any way to simulate the Polarization vs Electric Field loop of BaTiO3 using Quantum ESPRESSO?

I'm new to the Quantum ESPRESSO package. There are articles outlining the procedure of indirectly simulating the P-E loop of piezo-electric materials via berry phase calculations.One procedure is ...
6
votes
0answers
25 views

What's the crystal orbital Hamiltonian population?

What's the crystal orbital Hamiltonian population (COHP) or the crystal orbital overlap population (COOP)? What's the relation between the bandstructure or density of states (DOS) and COHP/COOP? Why ...
6
votes
1answer
138 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....
5
votes
0answers
22 views

How to convert lab frame quaternions and plane normal to misorientation quaternion and crystal plane normal for grain boundaries?

Background Let qA and qB represent unit, orientation quaternions of grain A and grain B of a grain boundary in the lab reference frame, respectively. Let qm be the misorientation quaternion of qA and ...
6
votes
0answers
34 views

Evaluating $C_v$ for one mole $H_2$ molecules in a quantum simulation

Given an ensemble of $N$ diatomic molecules, we know that the rotational partition function is given by $$Z_r = z_r^N$$ where $$z_r = \sum_{l} (2l+1)e^{-Kl(l+1)}$$ where $K = \beta \hbar ^2 /2I$. I ...
8
votes
1answer
55 views

How to do spin polarization calculations using Quantum ESPRESSO?

I am currently new to DFT calculations in Quantum ESPRESSO. Though, I have read some research papers for determining spin polarization and Half-metallicity in certain Heusler alloys. These research ...
8
votes
5answers
495 views

How to know optimal K-points grid values for good DFT calculation?

I am doing DFT calculations with pw.x executable in Quantum Espresso. For this we have to choose right K-points grid in order to perform error-less calculation. But I have no idea about how can I ...
8
votes
1answer
91 views
+50

Predicting magnetic moment of a metal complex computationally

Recently, for entrance exams, I have been dealing with a lot of weird compounds. One of them is $\ce{K3[Mn(CN)6]}$. The objective was to predict the magnetic moment of the above complex. I predict ...
7
votes
0answers
28 views

How does MBD (MBD-NL) differ from DFT-TS?

Is anyone familiar with the Tkatchenko's new MBD-NL method? How does it differ from DFT-TS? I couldn't understand everything from the paper.
8
votes
2answers
119 views

How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?

I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
9
votes
1answer
71 views

How to build the matter modeling model with appropriate tools?

How to build the matter modeling model with appropriate tools? When we perform matter simulation with first-principles calculation, building a reasonable model always be the very first and important ...
7
votes
2answers
241 views

p-orbitals in STO-3G basis set

I look at the STO-3G basis set for Carbon atom (downloaded from the basissetexchange.org) and I see one set of exponents and two sets of coefficients for the p-orbitals. How do these exponents and ...
5
votes
0answers
52 views

Is this statement correct: “All structural variations are energy driven”?

In modelling using molecular mechanics can one state that "all structural variations are energy driven?". The statement is related to protein-ligand binding in modelling. Sometimes one can ...
8
votes
2answers
106 views

Are meta-GGA functionals SCAN (and its variants) ok to use in planewave DFT with the PBE pseudopotentials?

The meta-GGA SCAN functional has been there for a while. Despite the lack of SCAN (ultrasoft/PAW) pseudopotentials, various works used it in plane-wave pseudopotential calculations with ...
10
votes
2answers
376 views

When should spin polarized calculations be done?

Should the presence of a d block element in the unit cell mandate the need for performing spin-polarized calculations? I wanted to find out the DOS, PDOS, and the band structure. I'm new to DFT and I'...
6
votes
0answers
21 views

VASP's NPAR and KPAR for parallelization

What's the best way for parallelization in VASP for periodic systems? In the documentation, it mostly explains it for the local computer and molecule calculation. Apparently, these explanations don't ...
6
votes
0answers
31 views

Inconsistent data of chemical potential from different papers

I am looking for chemical potential from literature: ...
7
votes
2answers
201 views

acceptable range of stretching of a lattice unit cell when we do the heterostructure

Currently, I have to put two different materials together to form a heterostructure. I've already transformed the unit cell of material A from trigonal to cubic. Now the unit cell has a rectangular ...
7
votes
0answers
63 views

How to explain Density Functional Theory results to an experimentalist?

When we present our Density Functional Theory simulation results e.g. lattice parameters, stacking fault energies, band gaps, etc. to people who are experimentalists then the very first question ...
7
votes
2answers
59 views

Combined effects of strain and doping on the electronic structure of semiconductors

I've read papers in DFT studies on band gap tuning in semiconductors and the usually studied methods are either through doping or application of external strain. But it is always just one or the other....
9
votes
1answer
128 views

Computational biology textbook similar to “Computational Materials Science” by June Gunn Lee

I'm looking for a text for computational biology which is similar in structure to a book called Computational Materials Science by June Gunn Lee. In his book, Lee discusses the theory of MD ...
9
votes
1answer
335 views

High precision helium energy

In the paper "High Precision Theory of Atomic Helium", Drake lists the then best-known ground state energy of the Schrödinger equation for helium to 22 digits as: $$\lambda_0 \approx -2....
7
votes
1answer
47 views

Different energies for two different geometries where only the monolayer c lattice constant is different?

I carried out a simple single-point PBE calculation on two different graphene monolayers (only c is different) using VASP with 12x12x1 k-grid. Geometry 1: ...
6
votes
0answers
33 views

Choosing RAM, CPU time, # of cores, and other parameters for an MD run

I did an AIMD run in VASP using 64 cores (32 cores/node) and 250 GB of memory (125 GB/node) for 5 ps (1 fs time step). The calculation took 12.6 hours to complete. CPU efficiency was 99.7% and memory ...
10
votes
2answers
155 views

Band structure with additive dispersion methods

Let's say I optimized geometry with PBE+D3, does it matter if I make single point bandstructure calculation with just PBE or PBE+D3 since D3 is a additive method.
9
votes
2answers
124 views

Creating a heterostructure in VESTA

I have two different crystal structure and I want to create a heterostructure but the problem is that the shape of their unit cell is different. I know how to combine them if their unit cell are same. ...
10
votes
0answers
31 views

How exactly does one compute the vibrational density of states from the output of a molecular dynamics simulation?

There are many things that can be done with the output of a molecular dynamics simulation, but one of the more powerful things is the ability to compute the vibrational density of states (or the ...
13
votes
5answers
225 views

DFT software package for a beginner?

I would like to do start doing some basic calculations using DFT. I am interested in solid state physics of strongly correlated materials in 3D (for example high temperature superconductors) or 2D (...
7
votes
3answers
210 views

Molecular visualization software in Jupyter (IPython) Notebooks

Jupyter notebooks have always been a great way for me to create high-quality graphs, and write code. The features also continue to improve with packages such as Jupyter Lab, and now Jupyter Books, ...
11
votes
1answer
84 views

How to use coherent-potential approximation (CPA) method in VASP?

I found there are very few tutorials regarding how to use the CPA method in VASP. Are there any nice materials available? Also what are the pros and cons of CPA and VCA? If CPA is more reliable then ...
9
votes
1answer
37 views

How can I determine the maximum value of a spin orbital and its derivative in any direction?

I'd like to be able to recover the maximum value that any of the basis functions can take, as well as their maximum derivative. How can I do this? For context, I need it because I want to calculate ...
6
votes
0answers
44 views

What are the advantages/disadvantages of QMC over ACFDT-RPA?

I had some experience with the ACFDT-RPA, despite its promising features it's not practical most of the times, and for that reason, I'm looking for a new method for reference calculations. QMC is the ...
10
votes
1answer
154 views

Are QMC calculations practical for periodic structure calculations?

Even some DFT methods or beyond DFT methods such as MP2 calculations are computationally very expensive today even with clusters. If you compare QMC (quantum monte carlo) calculations with them, are ...
11
votes
3answers
171 views

How to determine whether we can put two semiconductor thin film together?

I am beginner of material modelling that's why my question may be basic and I have no direction. If we want to see whether two crystal layer(semiconductor) can be put together, can the DFT calculation ...
9
votes
2answers
65 views

What software can be used to do QTAIM analysis?

I have a rather general question of what software packages exist to do Quantum Theory Atom in Molecule (QTAIM) analysis of periodic and non-periodic systems. Working with Gaussian I have previously ...
7
votes
0answers
53 views

Constraining coordination or bond lengths for certain atoms in VASP

I have a structure composed of many MX4 tetrahedral units. When doing MD on this structure I find that just one M atom moves into a trigonal planar coordination (MX3). I was wondering how to set ...
9
votes
2answers
36 views

Analytic Hessians for meta-GGA functionals

In many of the free/open-source QM programs like GAMESS, ORCA, NWChem, the calculation of analytic hessians is not possible when a meta-GGA density functional is used, like M06-2X. My first question ...
6
votes
1answer
92 views

PySCF: atomic basis Fock matrix changes after mo_coeff update

I've noted a curious thing with PySCF when updating the molecular orbital coefficients of the mean-field object. If one prints out the Fock matrix in the atomic basis (...
6
votes
1answer
99 views

Velocity operator for a Hamiltonian that satisfies the generalized Schrodinger equation

The velocity operator is defined as $\mathbf{v}=i[H,\mathbf{r}]$ for the Hamiltonian $H$ satisfying $H\psi=\epsilon \psi$. This can be obtained from the Ehrenfest theorem. I'm wondering if $\mathbf{v}=...
9
votes
1answer
73 views

Monkhorst-Pack, Gamma-centred and gamma only

Sorry if this question is too simple for this community but I still couldn't find an answer to it. Do gamma-centred and gamma only grid mean the same thing? If not, what's the difference? How do they ...
10
votes
2answers
168 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 ...
9
votes
1answer
68 views

Partial density of states in random solid solutions

This question comes as a follow-up to https://mattermodeling.stackexchange.com/a/2214/116; nonetheless, it is relevant on its own as well. To designate a particular crystal structure to a random ...
7
votes
1answer
58 views

What are the methods for calculating interaction energies of layered materials, and where are they implemented?

What are the available methods for the calculation of reference interaction energies of layered materials and in which codes they are implemented? For example, I know RPA-ACFDT in the DFT concept. But ...
8
votes
0answers
30 views

Problem related to the calculation of elastic constant with VASP5.4.4

I am using VASP5.4.4 to calculate the mechanical properties of the cubic phase SnTe. The structure can be found in the materials project website. In detail, I use the following INCAR to calculate the ...
8
votes
2answers
92 views

Evaluate the orbital magnetic dipole moment within the PAW sphere

In general, the orbital magnetic dipole moment operator is defined as: $$- {e\over2} \mathbf{r \times v} \tag{1}$$ $\mathbf{v=p}/m$ is true only for simple Hamiltonian like $-1/2\ \nabla^2+V$, but not ...
9
votes
0answers
58 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 BSE Is there a ...

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