I get this question time to time,
how does a nuclear magnetic resonance property like chemical shifts are calculated by Quantum Espresso? How do you simulate the nuclear spin?
The thing is, for the chemical shifts (calculation='NMR') , the level of assumptions we make in QE-GIPAW leave us totally free from simulating the nuclear spin. What we look at is how the electronic structure induces a magnetic field at nuclei position.
So, within the limits of the theory, everything depends on the surrounding electronic structure. The code does not have to know if it is X113 or X112 isotope..
Lets say you are looking at the chemical shifts of boron, B10 or B11 does not make any difference to the code, at least not for the chemical shifts, sigma(iso)
But of course if you have a nuclei with spin > 1/2; you need to know which isotope you are dealing with to continue with nuclear electric quadrupole interactions, namely the Cq's and eta's as commonly denoted. Back to Boron, B10 has double the moment of B11 but 1/5th of natural abundance. So just remember to input these parameters in your electric field gradient (EFG) calculations when dealing with isotopes with with spin > 1/2 through keywords q_efg(i) for element i.
Damn simple :)
ps: i check webelements for q_efg's, under NMR properties. Here is Boron: http://www.webelements.com/boron/nmr.html
pps: Natural abundance matters. Remember to check that and average as needed. EFG calculations are very cheap anyways.
ppps: Unit of electric quadrupole moment in quantum espresso gipaw routine is [ electron*10e-30 meter ^2 ] not [electron*milibarn]. The conversion is straighforward: Find the milibarn value, divide by 10, input in Quantum Espresso q_efg. Come on I cannot help more than this :)
how does a nuclear magnetic resonance property like chemical shifts are calculated by Quantum Espresso? How do you simulate the nuclear spin?
The thing is, for the chemical shifts (calculation='NMR') , the level of assumptions we make in QE-GIPAW leave us totally free from simulating the nuclear spin. What we look at is how the electronic structure induces a magnetic field at nuclei position.
So, within the limits of the theory, everything depends on the surrounding electronic structure. The code does not have to know if it is X113 or X112 isotope..
Lets say you are looking at the chemical shifts of boron, B10 or B11 does not make any difference to the code, at least not for the chemical shifts, sigma(iso)
But of course if you have a nuclei with spin > 1/2; you need to know which isotope you are dealing with to continue with nuclear electric quadrupole interactions, namely the Cq's and eta's as commonly denoted. Back to Boron, B10 has double the moment of B11 but 1/5th of natural abundance. So just remember to input these parameters in your electric field gradient (EFG) calculations when dealing with isotopes with with spin > 1/2 through keywords q_efg(i) for element i.
Damn simple :)
ps: i check webelements for q_efg's, under NMR properties. Here is Boron: http://www.webelements.com/boron/nmr.html
pps: Natural abundance matters. Remember to check that and average as needed. EFG calculations are very cheap anyways.
ppps: Unit of electric quadrupole moment in quantum espresso gipaw routine is [ electron*10e-30 meter ^2 ] not [electron*milibarn]. The conversion is straighforward: Find the milibarn value, divide by 10, input in Quantum Espresso q_efg. Come on I cannot help more than this :)
No comments:
Post a Comment