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Results tagged with quantum-chemistry
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user 5
For questions about quantum chemistry.
13
votes
Accepted
What does "level of theory" mean?
Tristan's answer explains what B3LYP and 6-31G(2df,p) are. I agree with everything Tristan said, I will just write an answer that is a bit more generic: not specific to B3LYP and 6-31G(2df,p).
"Level …
2
votes
What are the observables when a quantum system is comprised of orthogonal spacetimes?
Preamble
After Susi's vote to close this question:
"I’m voting to close this question because this belongs in the physics network."
I inquired with a Physics.SE diamond moderator to see whether or n …
13
votes
Accepted
How is MCTDH derived?
I will outline the way it was derived in the original 1990 paper. We start with an ansatz for the time-dependent wavefunction:
\begin{equation}
\tag{1}
\psi(x_1,\ldots,x_n;t) = \sum_{j_1=1}^{m_1}\cdo …
13
votes
Is it better for me to study chemistry or physics?
As someone who did his undergrad in Canada, PhD in UK, and acquired post-PhD research experience in Japan, Singapore, USA, Germany, and again in Canada: I can say that the dilemma you're facing is a m …
5
votes
Has there been any research on the stability of buckminsterfullerene?
"Has there been any research on the stability of buckminsterfullerene?"
There is, for example, this paper with title "Stability of Buckminsterfullerene, C60". It has almost 100 citations.
"Has it b …
8
votes
Accepted
Critical difference and roles of Slater- and Gaussian-type orbitals
"My question is that, does the GTO simply represent the STO by using many Gaussians, or not?"
There does exist the STO-nG basis set family in which $n$ Gaussian orbitals are fitting to represent a s …
7
votes
Why are method developments and new implementations not done much in Gaussian?
"Is Gaussian too old, the code too deprecated or are there copyright issues?"
You mentioned "copyright issues" but papers that are publicly available in academic journals are not subject to the type …
9
votes
What does “strongly correlated” mean?
You got it completely correct when you said:
"it seems that the definition of it is ambiguous and sometimes inconsistent in different field of study."
As the other answers show, it's a bit of a "loo …
4
votes
How to use libint with Python
Some background:
The following answer by Anycorn was "accepted" by the OP:
"I wrote python bindings for libint. Did you look in python/tests? there are two tests, including sample hf program"
but it …
3
votes
How to choose the number of roots in a CASSCF calculation?
The term "roots" refers to the number of "electronic states". If you are only interested in the ground state, then you are seeking 1 root. If you want the ground state and the first 4 excited states, …
11
votes
DFT functionals from MP2 methods
Susi is right that these are called double hybrids, I'll just add a bit more to complement that correct answer. My answer to "What are some recent developments in density functional theory?" was about …
6
votes
CCSD and CISD size-consistency problem
CISD is not size-consistent for more than two electrons, and CCSD is size-consistent and size-extensive for any number of electrons.
With CCSD, if you calculate the $\ce{Li2}$ energy for a bond length …
7
votes
Have quantum computers been proven to speed up any matter modeling algorithm?
FCI (Full Configuration Interaction)
The FCI expansion of a wavefunction allows us to obtain the exact energy of a system given a basis set with $N$ spatial orbitals. On a classical computer, for a si …
1
vote
FCIDUMP file from UHF calculation in PySCF
The code for this function
For NECI, a Python function was made for writing an FCIDUMP file after a UHF calculation, and it can be found at line 308 of this file (the resulting FCIDUMP file can be use …
12
votes
Accepted
High precision helium energy
The 2006 variational calculation by Schwartz is lower (more accurate) than Nakashima & Nakatsuji's 2007 energy:
2006 Schwartz: -2.903724377034119598311159245194404446696925309838
2007 Nak …