# Questions tagged [ab-initio-calculations]

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

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### Setting a frozen core in Molpro

I am carrying out a project which involves obtaining the RHF result and the integrals for the chromium dimer (Cr2) under Ahlrichs' SV basis. In the literature against which we attempt to benchmark, ...
151 views

### What information does the 1RDM contain?

The one-electron reduced density matrix (1RDM) contains information useful for the prediction of molecular properties (for instance, dipole moments). As an example, the 1RDM can be easily obtained in ...
• 1,829
75 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 ...
• 201
69 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 ...
• 131
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### 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 ...
• 201
103 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 ...
84 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 ...
• 201
38 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 ...
80 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 ...
548 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 ...
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### 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-...
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### 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 ...
• 91
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### 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?
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143 views

### ORCA: Dipole moment of LiH from SP calculation

I calculate LiH with ORCA ...
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### 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 ...
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### 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 ...
158 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 ...
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### 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 ...
• 2,361
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 ...
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