Questions tagged [quantum-chemistry]
For questions about quantum chemistry.
191
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ORCA Error: NCalcs not set
I've been getting the following error whenever I use CCSD(T) and the ORCA Forums don't have an answer to this one:
...
- 21
4
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1
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344
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Kill or let be: Is this calculation stuck or just very slow?
My question is regarding a medium-to-large DLPNO-UCCSD(T)-F12 calculation.
I have a ~250 electron system, an open-shell molecule inside a water droplet, and I'm trying to get the total energy, first ...
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9
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Software for quantum electrodynamics?
I've been reading some beginner books about quantum electrodynamics / quantum field theory (e.g. Feynman's QED book), and basically everything is done at the paper and pencil level.
I'm curious if ...
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0
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Change bonding thresholds in NBO Calculations?
I'm looking at a system with really long bond lengths, and I'm trying to determine if there's any interaction at all between orbitals on two particular atoms.
I'm using NBO7 with the GENNBO interface, ...
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Is it okay to use semi-empirical methods to optimize structures if I perform high-level energy calculations?
For non-covalent systems comprised of small-molecule monomers, folks are usually interested in understanding the interaction and binding energies of small (gas-phase) clusters ... things like $\ce{X(...
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Comparison between the ordering of Molecular Orbital coefficients between Gaussian and PySCF
I am trying to compare the Molecular Orbital coefficients obtained from PySCF and G09 program. Below is the PySCF and Gaussian input and output. I am using 3-21G basis and RHF method for both the ...
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2
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72
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Analytical derivative of nuclear-electron attraction integrals over gaussian functions
I'm currently writing a program which evaluates the first derivatives of molecular integrals (over gaussian basis sets) with respect to the cartesian coordinates of the nucleus. I'm somewhat stuck ...
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217
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Which is better for binding energies: DFT-D3 or RI-MP2?
I am trying to calculate the binding energy of a small molecule with an underlying surface. I have used B3LYP-D3BJ (as implemented in ORCA) at def2-TZVP basis set to optimize the geometry of the VdW ...
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3
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1
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85
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Repeated Error message ORCA
I am repeatedly getting the error message:
[file orca_main/maininp1.cpp, line 17547]: ERROR: expect a '$', '!', '%', '*' or '[' in the input
when I run my Orca script.
My inp file looks like:
...
9
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1
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751
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Why is chemical bond dissociation difficult to simulate?
I'm a student doing quantum computing research trying to understand better what kinds of chemical systems are difficult to simulate on a classical computer and for which quantum simulation could be ...
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Why, if the potential is different from the Coulomb one, but has spherical symmetry, the eigenvalues of the system are non-degenerate? [closed]
Question duplicated from here https://mathematica.stackexchange.com/questions/287433/why-if-the-potential-is-different-from-the-coulomb-one-but-has-spherical-symme and here https://physics....
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NLMO algorithm failed to converge
I have been using NBO 7.0 software and the file.47, and the option in ORCA with nbo block and sometimes I have problems with the convergence algorithm for NLMO specifically this error: NLMO algorithm ...
4
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0
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33
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How to compute only part of molecular Hessian accurately (hybrid Hessian or partial Hessian calculation)?
Hessian is required for minimisation and transition state (TS) optimisation algorithms. While the full Hessian at a certain level of theory is calculated usually for TS optimisation, usually ...
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PC Specifications for a small DFT Research Group [duplicate]
Planning to set up a small research group here at my university to do some DFT/MD work and I'm looking for a nice setup that will cater to that. Will be asking for funding from the university or from ...
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2
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How to remove f functions from a cc-pVQZ basis set in CFOUR format?
I need to perform a calculation on a BN system with using cc-pVQZ stripped of the f functions. However, I don't really know how to do this and I have not been able to find a revised one already. I ...
- 536
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141
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Help with Mathematica for optimizing a Gaussian basis set for a hydrogen atom in a magnetic field
This is a follow-up to my previous question: Optimal Gaussian basis set for hydrogen atom in magnetic field
Brief description of the problem
I would like to find the ground and excited states of the ...
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6
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1
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Compute polarizability after each step of relaxed scan in Gaussian 16
I am computing a relaxed 2D scan with Gaussian 16 in order to reproduce some computational data. I am interested in computing the dipole moment vector and the (static) polarizability matrix after each ...
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A terminology for QM calculation methods
I wonder if there is any terminology (or name of classification) that refers to ab-initio QM methods based on the Schrodinger equation and basis functions, such as HF and post-HF methods, but not DFT ...
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138
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Optimal Gaussian basis set for hydrogen atom in magnetic field
Copy from here https://mathematica.stackexchange.com/questions/285044/optimal-basis-set-of-gaussian-functions-for-describing-a-quantum-system
This question arose during the discussion of the previous ...
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75
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How can one determine the time-step for imaginary time evolution?
The real-time evolution of a quantum system described by the state $\psi(t)$ is formally given by,
$$ \psi(t+\Delta t) = \exp^{- i \hat{H} \Delta t / \hbar} \psi(t)\tag{1}$$
For dynamical simulations ...
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Scanning two bond lengths G-16
If a scan is performed over two CVs, or collective variables (bond lengths here), does the code simultaneously step through both of the CVs or does it step through the first one, and scan the second ...
9
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325
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Usual way of computing exchange-correlation potential on a simple case H2 (RKS, LDA)
The python code is here.
I tried to do a DFT calculation for H2 Restricted Hartree-Fock with Local Density Approximation. The optimization is a scf-loop with Lagrange-multiplier only. I use the same ...
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2
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Computing the rotational entropy in RRHO approximation
I am implementing the computation of Gibbs energies by their molecular parameters (structure, frequencies) in my program Chemcraft (the main task is the possibility to cut small frequencies which ...
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4
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59
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How To Extrapolate Ground State Energy in Thermodynamic Limit via DMRG
I am implementing a system of fermions in a trap potential with tensor networks and want to find the ground state energy via DMRG (I'm using SyTen). As usual in quantum chemistry the Hamiltonian has ...
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What is the X in Almlöf and Taylor's "Unified treatment of energy derivatives?"
I have been studying the possible methods for basis set optimizations. One notable paper is "Energy-optimized GTO basis sets for LCAO Calculations. A Gradient Approach" by Knut Faegri Jr. ...
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77
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PySCF calcuation of 'one-index' electrostatic (Hartree) potential
I'm trying to calculate the electrostatic (Hartree) potential corresponding to a single (auxiliary) GTO:
$$v_i({\bf r_1}) = \int d{\bf r}_2~ \frac{\phi_i ({\bf r}_2)}{r_{12}}$$
[Please note that $\...
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3
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62
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Computation of thermodynamic functions of molecules by molecular parameters
I want to implement in my program Chemcraft the computation of entropy and Gibbs energy of molecules in approximation "rigid rotor - harmonic oscillator", by the molecular parameters (...
- 326
3
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1
answer
427
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VASP calculation error
I got the error when running Vasp Calculation: Error EDDDAV: Call to ZHEGV failed. Returncode = 11 1 1. Can any one help me solve this problem?
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What is the lifetime of propane at standard conditions transitioning from an excited rotational state back to ground state?
I am a retired microwave engineer (88 yrs old) and have not had the opportunity to study or learn anything about quantum physics. I designed and built radars for the military.
We found a claim that ...
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2
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90
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Understanding the complexity of geminal-based wavefunctions
Cross-posted on Reddit.
I have been reading through [1] to get a better understanding of geminal-based methods. Some short passages are included below:
The occupation of each orbital in the expansion ...
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4
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1
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58
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How to apply solvent-correction to Gaussian derived Gibbs energies?
I study reaction A + B → C + D in a water using DFT. I think I should apply some kind of correction over RRHO because it is not true in a solvent. I found the given work (https://doi.org/10.1021/...
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174
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Understanding derivation of geminal based methods [closed]
Cross-posted on Reddit.
I have been reading through [1] to get a better understanding of geminal based methods. This is one of two questions that I'm asking about that paper on this site, the other ...
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ORCA failed during NEB-TS ONIOM
Thanks in advance for any help provided. I was trying to find the transition state of a diels alder reaction and considering my system's bulkiness I wanted to try a NEB calculation considering part of ...
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3
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1
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135
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Is PySCF able to print checkpoint files during a CISD calculation?
The problem
I've described how to restart a CISD calculation in my answer to the question: Restarting an FCI calculation in PySCF, but this requires all iterations of the CISD calculation to finish, ...
- 33.1k
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3
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Energy of each fragment in ORCA?
After the definition of the fragments in the geometry section of the calculation, is there a method to call, or a keyword to turn on, in order to obtain the energy of the fragments themselves?
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4
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0
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Obtaining data for plotting Fermi and Coulomb holes of a hydrogen molecule
I need to visualize the exchange (Fermi) and correlation (Coulomb) hole of a hydrogen molecule to qualitatively illustrate the compensation of of both holes to form the total hole that is localized ...
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4
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Does anyone know where and how I can download and install Spartan (the Molecular Modeling software)?
I've been given the task to calculate the energy of the lowest unoccupied molecular orbital (eLUMO) using Spartan but I'm not really familiar with the said software, can anyone tell me a bit of an ...
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How to choose the number of roots in a CASSCF calculation?
What are the criteria that one has to consider while chosing the number of roots in a CASSCF calculation?
3
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1
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387
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How to compute free energy for solvation using gaussian09?
I'm trying to compute the free energy of solvation of a molecule in gaussian09 using the continuum solvation model, but I am haveing difficulties, I don't know how to do it and gaussian manual does ...
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MOLPRO: is there an analogue of the Gaussian FCHK file?
With the Gaussian quantum chemistry program, I usually generate formatted checkpoint files (.fchk) that I then use to perform different atom-in-molecule analyses. I am currently facing the need of ...
- 151
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Molecular Basis set construction (STO-3G) for BeH2
I have a rather basic question about the (minimal) number of molecular orbitals that are needed for some computation work on the BeH2 molecule.
To my understanding, STO-3G forms a minimal basis set, ...
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2
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570
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How to use libint with Python
I am trying to write a basic Hartree-Fock code to compute orbital energies and total energy of a molecule at almost all basis sets. I wrote the integral code in Cython/Python and is very slow. I would ...
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Can a MO energy computed from a HF or DFT calculation for one molecule be directly compared to that of another molecule?
This was inspired by a recent question How is the zero energy defined for molecular orbitals? which made me pause to think if I understood clearly or not about the zero of energy of an MO.
For example,...
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261
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Unrecognized or duplicated keyword error using ORCA DFT calculations using avogadro
I'm using Avogadro to generate an input for ORCA, however, when I'm trying to run that input in ORCA it says:
...
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How to calculate the number of interstital electrons from Quantum Espresso charge density outputs?
I have calculated the charge densities (in 1D, 2D and 3D formats) with the help of Quantum Espresso DFT.
The system (/material) is simple, two atoms in an unit cell.
However, I want to determine the ...
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190
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Binding energy with ONIOM
Do you know how to compute binding energy using Gaussian? I have optimized binding pocket with ligand using ONIOM methodology implemented in Gaussian16. For the high layer B3LYP/6-31+G(d,p) was used, ...
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28
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Book that can interpret molecular properties of organic coumpounds? [closed]
I'm new in the field of research and modelling matter.
I got results from DFT calculations but I don't know how to interpret them and I wonder if anyone can suggest to me books for interpreting ...
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Convert reduced density matrix in A.O. basis from GAMESS to pyscf [closed]
I want pyscf to read the single-particle reduced density matrix computed by GAMESS.
However, I am having trouble because the matrix sizes in GAMESS and pyscf are different.
For example, the AO-...
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1
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How to use GIMIC for "line integral convolution on a surface" in ParaView?
I am using GIMIC for evaluating DFT-calculations of aromatic compounds and visualizing magnetically induced aromatic ring currents. There is a nice way of visualizing them via a so called stream line ...
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1
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Importance of orbitals other than HOMO and LUMO
I know that the HOMO, LUMO, and its gap are useful in understanding the physical properties and chemical reactions of molecules.
Here, are there any phenomena in physics or chemistry that other ...
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