All Questions

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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....

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 ...

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 ...

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 ...

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 ...

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 ...

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.

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 ...

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 ...

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 ...

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 ...

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 ...

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'...

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 ...

I am looking for chemical potential from literature: ...

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 ...

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 ...

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....

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 ...

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....

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: ...

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 ...

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.

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. ...

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 ...

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 (...

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, ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 (...

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}=...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...