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pH13
pH13
10:25
@M.Ibrahim today (as weekend is over) we can figure it out
pH13
pH13
10:52
now I'm at lunch for 1 hour
 
6 hours later…
M.Ibrahim
M.Ibrahim
16:31
What is your job ?
pH13
pH13
16:49
hello
@M.Ibrahim what is my job?
M.Ibrahim
M.Ibrahim
17:08
what do you work ?
only research ?
or work at university beside ?
pH13
pH13
17:37
as I wrote, I'm doing my master thesis on university
@M.Ibrahim
M.Ibrahim
M.Ibrahim
so you are full-time researcher
pH13
pH13
kind of, yes
can you repeat the question that you had the other day?
M.Ibrahim
M.Ibrahim
that about the difficulties in your thesis ?
pH13
pH13
no ... the one regarding basis sets. that's why I opened this room
M.Ibrahim
M.Ibrahim
You said that there is no basis set for a molecular orbital
I don't get this !
pH13
pH13
17:51
maybe I am nitpicking or am wrong .. I don't know ... :D
M.Ibrahim
M.Ibrahim
but I was misunderstanding the orthonormality of wave functions as orthocresol said to me
pH13
pH13
basis sets consist of basis functions that somehow describe the atomic orbitals
M.Ibrahim
M.Ibrahim
yes
pH13
pH13
combining the atoms into molecules doesn't change this
so basis sets describe the atomic orbitals of atoms
M.Ibrahim
M.Ibrahim
combining atomic orbitals result in MO
pH13
pH13
17:55
those atoms then describe a molecule, so the molecular orbitals are described through a combination of atomic orbitals which are constructed through the basis set, but that does not say that the basis set is for molecular orbitals
do you know what I mean?
M.Ibrahim
M.Ibrahim
how many basis sets are required to form a molecular orbital ?
pH13
pH13
that question makes no sense
you have a molecule which consists of atoms
each of those atoms has it's atomic orbitals which are described by the applied basis set
and linear combinations of those atomic orbitals (LCAO) are then constructed to describe the molecular orbitals of the molecule
M.Ibrahim
M.Ibrahim
LCAO and basis set is the same thing
So there is only one basis set for that describe the MO based on the AOs that form it
pH13
pH13
@M.Ibrahim how can a method and a list of functions be the same?
M.Ibrahim
M.Ibrahim
This in case of reactivity prediction not the atomic spectra prediction
I may be wrong, definitely you are more expert than me .
pH13
pH13
18:13
don't say that ... I am searching for a good example
M.Ibrahim
M.Ibrahim
There is something missing in my picture ..
pH13
pH13
if you actually take atomic orbitals as those from the solution of the schrodinger equation, you might be right
those atomic orbitals can be described by so called slater-type orbitals (STO)
but when considering a molecule with more than 2 atoms you will need to calculate four-center integrals which need a lot of time when using the STOs
so usually one does not use STOs but gaussian-tape orbitals (GTO)
but that leads to another problem
M.Ibrahim
M.Ibrahim
That is right .
What is it ?
pH13
pH13
you need a lot of GTOs to describe a single STO
and a basis set of today consists of coefficients and exponents for those GTOs for a fixed set of elements
M.Ibrahim
M.Ibrahim
yes a set of constants for each element
obtained from experimental data
pH13
pH13
18:27
not really, no
mostly from calculations
M.Ibrahim
M.Ibrahim
Ok
but the thing I don't get is that how the basis set is formed of orthogonal AOs ?
pH13
pH13
it was a constrained when they were calculated
M.Ibrahim
M.Ibrahim
in the same time it is required to describe an MO of different atoms !
pH13
pH13
exactly
if I remember correctly, orthocresol said it
M.Ibrahim
M.Ibrahim
don't you have any problem with this ?
pH13
pH13
18:35
that is, because those atomic orbitals are orthogonal on every atom of the molecule but don't need to be orthogonal on two different atoms
when you take H-F, you have atomic orbitals on H and different atomic orbitals on F
the AOs for H are orthogonal to each other and the AOs on F are orthogonal to each other. but the AOs on H are not orthogonal to the AOs on F
what time is it now for you?
M.Ibrahim
M.Ibrahim
the basis set is constructed to describe the H-F MO , right ?
it's 8.40 pm
pH13
pH13
the basis set is constructed to describe the AOs on H and F, which are then combined to describe the MO on H-F
M.Ibrahim
M.Ibrahim
H has a basis set , F has a different basis set and H-F has a basis set formed by adding the formers ?
pH13
pH13
that should be the case. look at slide 3 southampton.ac.uk/assets/centresresearch/documents/compchem/…
I will go in about 15 minutes but will be online again tomorrow from 10 or 11 am to 5 or 6 pm (your time zone).
brb
M.Ibrahim
M.Ibrahim
ahaa, so the basis set is not entirely consists of orthogonal AOs
tyt
thank you very much @pH13
pH13
pH13
18:49
@M.Ibrahim so to say
the AOs only need to orthogonal on every single atom
M.Ibrahim
M.Ibrahim
although it is logical to say that but there is no any textbook I read emphasized this
and i was wondering how will be overlap between independent wavefunctions
pH13
pH13
:)
so ... see you tomorrow for more questions ;) have nice evening
M.Ibrahim
M.Ibrahim
ok good bye :)
privetDruzia
privetDruzia
19:40
Hello @pH13

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