All Questions
Tagged with quantum-chemistry ab-initio
30
questions
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49
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Critical point from ab initio calculations
I was wondering if it is possible to calculate the critical point (e.g., temperature, pressure, and density) other than via experiments or equations of state like ab initio calculations.
Would anyone ...
- 311
6
votes
0
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71
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Are there examples of publications using DFT instead of HF as a coupled-cluster reference?
I have been searching for a while, and only managed to find an article by M. Saitow,[1] where CAM-B3LYP orbitals are used. I was wondering if this has been done elsewhere.
It was recommended to me by ...
- 61
3
votes
2
answers
427
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Effective core potential and Gaussian basis set
Is using the effective core potential (ECP) and Gaussian basis set simultaneously in ab initio calculation a valid approach? For example, is it correct to use ECP for one of the atoms and, instead of ...
- 123
2
votes
0
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162
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Potential energy surface in transition state theory
I would like to study the typical reaction from the transition state theory:
$$\ce{AB + C <=> ABC^‡ -> A + BC}$$
Assuming $\ce{ABC^‡}$ is a colinear molecule, the potential energy surface of ...
- 309
1
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0
answers
95
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How to plot the wave function after a Hartree-Fock calculation?
I have written a code in Mathematica and have obtained the final energy of the hydrogen molecule. I have used Gaussian basis functions for this calculation. Now I need to plot the ground state wave ...
- 285
6
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1
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181
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Is there a rule of thumb to predict when coupled cluster might dip below the variational limit?
Coupled cluster is a non-variational method, meaning that it can give energies that are below the true FCI energy (the "variational limit" for variational methods).
Often coupled cluster ...
- 1,452
1
vote
1
answer
397
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What are the steps of Hartree-Fock Theory?
Outline the steps involved in the Hartree–Fock method for the calculation of molecular electronic structure.
I understand the basics of HF, in that it does not account for electron correlation (...
- 348
1
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0
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63
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Calculating the Molecular Orbitals of a Molecular State [closed]
I am performing ab initio calculations on a heteronuclear diatomic compound using the MRCI method on the MOLPRO quantum chemistry package. I obtained the molecular states of the compound but I was ...
- 167
0
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1
answer
125
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Ab Initio and Molecular Orbitals [closed]
What is the difference between ab initio calculations and molecular orbital theory?
- 497
2
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0
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38
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Guide to DFT functionals [duplicate]
Having recently begun studying Quantum and computational chemistry in depth... I am looking for a manual, text, or guide of any form that could explain the basic formulations and potential of the ...
- 21
6
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0
answers
383
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How to evaluate the expectation value of the Hamiltonian for a three electron Slater determinant?
I'm having trouble with a few concepts dealing with slater determinants and many electron systems. In particular, when dealing with 3 electron systems, I know that
$$
\psi_0 = \frac{1}{\sqrt{6}} \det
...
- 61
3
votes
1
answer
277
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Why is the active space for the dinitrogen cation defined this large in my example?
I have a Molpro script which computes $\ce{N2^+}$ potential energies.
The significant part is the input for the wave function:
...
- 1,267
12
votes
1
answer
1k
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Why is Coupled Cluster not variational?
It has been noted in several sources (e.g. J. Romero et al. Strategies for quantum computing molecular energies using the unitary coupled cluster ansatz. arXiv:1701.02691 [quant-ph]) that one of the ...
- 1,696
3
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0
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178
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Bond order analysis in molpro
I'm trying to compute bond orders in a molecule, let's consider S2 as an example. I'm not entirely sure what's the right way to do that, but I assume NBO (Natural Bond Orbital) should give me what I ...
- 161
4
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530
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What all computing knowledge should a computational chemist traditionally have? [closed]
If I want to develop algorithms or computer programs for studying chemical systems, where should I start? Is learning one or two programming languages like FORTRAN enough? And if I do it, then how do ...
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