# Search results

1. ### Source of light

Hello, If we consider a source of light (in a point x), is it wright to say that the intensity decreases in 1/r2 ? Thank you !
2. ### DFT vs. HF (time argument)

Hi everyone, How hybrid functional can be quicker than HF ? Because we have to use the HF exchange part, so we have to solve the problem with HF before, am I right ? Thank you
3. ### Basis set QM

And how can we explain to use a 6-31G basis set to study a molecule like H2 ? 6 gaussian for the 1s and what about the splitting in 3+1 ? Thank you again
4. ### Basis set QM

Hello ! When we say that we use a 6-31G for a molecule (ex: N2), it is this number of gaussian (6+3+1) for both of the atoms or for each atom ? Thank you
5. ### DFT exchange energies

There is something I don't get... If we have to use exchange energy from HF in hybrid functional, how is it possible to be quicker than only HF? We have to solve HF calculation and then kohn sham, right ? Thank you for all these precision
6. ### Type of laser -- which is easiest to make?

If we consider a 3 level laser, we have to avoid absorption from level 1 to 2 (if it lase between 3 and 2). So, I'm asking if it is possible to not reflect the hν12 which is made by the spontaneous emission between this 2 level ?
7. ### Type of laser -- which is easiest to make?

Yes you're right, it's another thing. I just want to know if it is possible to avoid some reflection (in the gain medium) ? can we modulate the miroir to absorb (and so not reflect) some frequencies ?
8. ### Type of laser -- which is easiest to make?

And, just to be sure, is it possible to avoid the reflection of some frequency during the wall plug ? To be able to have only the frequency of the laser transition and avoid transition from the ground state (to maintain the population inversion).
9. ### DFT exchange energies

I thought that solving a problem with hybrid functional was quicker than with HF ?
10. ### Type of laser -- which is easiest to make?

@mfb Just easier if we talk about the energy of the light involved. (not about the material, juste suppose that you have access to anything) Is it true to think that's MASER because of the proximity between the level involved ? If we look at the boltzmann distribution, ΔE is smaller with maser...
11. ### Type of laser -- which is easiest to make?

Hello, Which type of laser are easier to make ? Micro-wave (MASER), infrared, visible light, UV... ? Which type of light leads in an easier way to a population inversion ? Is it maser because the level energy involved are closed ? Thank you
12. ### DFT exchange energies

Thank you for that explanation ! So, if results (using B3LYP) are worst because of HF exchange it's due to the fact that take EXC = EX + EC is an approximation ? And it's for the same reason that we cannot only take EX from HF exchange for hybryd functionnal ? Do you know why we get best...
13. ### Stuttgart ECP

In this article it's maybe more clear : (ctrl+F and SDD) http://www.udel.edu/chem/polenova/PDF/Polyoxometalates/W_CS_CPL2000.pdf
14. ### Stuttgart ECP

You're right ! ECP = electron core potential And the SDD I don't know what is it... On this site you can find the SDD and Stuttgart but I don't understand what is the difference between the 2 to be able to understand what means if we say that we take a Stuttgar t effective core SDD basis set...
15. ### Stuttgart ECP

Sorry I made a mistake it's not EDP but of course ECP (for SDD)
16. ### Stuttgart ECP

Hello ! I don't really undestand the difference between these two terms. Stuttgart Librairy is a pseudopotential, right ? What is SDD? (I've seen that this is a EDP too is that ok?) So what does that mean if we say that we take a Stuttgar t effective core SDD basis set ? What is the difference...
17. ### Laser effect

@DrClaude I mean if we can operate a population inversion (condition to make a laser) with visible light, IR, Micro wave, RX,... ? Or does limitations exists ? If we observe a population inversion with a MASER (MW), the population inversion will be between 2 levels with a small difference of...

anyone ?
19. ### DFT exchange energies

Hello ! How does the inclusion of a fraction of the HF "exact exchange energies" in an hybrid functional (B3LYP for example) can degrade the quality of the results ? I mean that the results are worst than expected because of the HF exchange, but if we call it "exact" how is it possible ? Thank...
20. ### Laser effect

No other opinion about that ?
21. ### Laser effect

Thanks for the answer. The three level I consider are like in this video at 0:50 . I guess that we can make a laser with any type of radiance (LASER with microwaves exists = MASER) I don't know if anyone has an opinion about that, is there any limitations about the incident light to produce a...
22. ### Laser effect

Hello, Can we make a laser with any type of radiance (IR,UV,visible,microwave,..) ? If we consider a three level system for example. In such a system, how can we avoid absorption from level 1 to level 2 ? Is it by choosing atoms/molecules in which the level 2 is greater than the fundamental ...
23. ### HF / DFT

Thank you for your answer. And what about the electron correlation? If we use DFT after HF method we can introduce the electron correlation whereas if we begin with DFT we can lose it by using HF, am I wrong?
24. ### HF / DFT

I've read an article about computational chemistry in which the authors were performing a geometry optimization. For this purpose, they firstly optimized the geometry at HF/6-311++G(d,p) level with full relaxation on the potentiel energy surface (what does that mean exactly ? Can we extract this...