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22 votes

What is the largest system that has been studied by the coupled cluster method?

ORCA The local pair-natural orbital (DLPNO) based coupled cluster method have been managed to investigate large organic molecule and small proteins (linear C150H302 (452 atoms, >8800 basis ...
Paulie Bao's user avatar
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11 votes

What is the largest system that has been studied by the coupled cluster method?

I’ll expand on this later but here is the abbreviated version. CTF The CTF code can do very large iterative CCSD and CCSDT using a dense spin-orbital formalism. CCSD up to 55 (50) water molecules with ...
Jeff Hammond's user avatar
10 votes

What is the largest system that has been studied by the coupled cluster method?

Localized natural orbitals methods allow tackling huge system sizes; some links were already given above. Of course, the accuracy remains sometimes a question in such methods: the methods rely on ...
Susi Lehtola's user avatar
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8 votes
Accepted

Calculating hyperpolarizability in NWChem

Major Issue The major issue here is that NWChem doesn't support second-order response in the DFT code: "Response calculations are currently supported only for order 1 (linear response), single ...
Jeff Hammond's user avatar
8 votes

Understanding emission spectra using TDDFT calculation

In general, you should use the $S_1$ state by default, unless you have reasons to suspect that your molecule is anti-Kasha. IMHO satisfying one of the following criteria guarantees that your molecule ...
wzkchem5's user avatar
  • 9,670
7 votes

Quantifying relativistic effects in DFT calculations

In reality, the contribution to an energy due to relativity, would be the difference between the "exact" energy with a model that captures all relativistic effects, versus a model that ...
Nike Dattani - No Free Time's user avatar
5 votes
Accepted

Energy per unit cell in NWChem differs for different supercells despite the same k-points density

It turns out, that NWchem do not support K-points with Gaussian basis. The nwpw section in my input files, that contains the K-point grid specification, actually ...
user36313's user avatar
  • 730
5 votes

Understanding absorption spectra using TDDFT calculation in NWCHEM

You should consider the states (roots) with non-zero oscillator strength. It means that the transition from the ground to excited state is allowed by the transition dipole moment rule. So, in your ...
Meilani Wibowo's user avatar
4 votes
Accepted

How to properly compute volume bound by surface with uniform electronic density, from data in a cube file?

Your solution is fine in principle, but skirts over a problem in the data: the volume enclosed by the 0.001 boundary is not enclosed within the bounds of the grid a.k.a. watertight! You can generate ...
lewiso1's user avatar
  • 936

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