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jjbjjb 

value and unit of dipole moment

Dear All,
I want to get the value of the dipole moment of a molecule. I used the following perl script:

my $length = $setMolecule->DipoleMoment->Length;

Is this length in the unit of e-A? Or if I was wrong, is there another way to get the value of the dipole moment?

Thank you!

All the best,
Jingjing

CarstenCarsten (Accelrys) 
Which Materials Studio version do you use? up to Materials Studio it as e\AA now it is in Debye.

Which kind of dipole moment is this? Where do the charges come from?
jjbjjb
Hi Carsten
Thanks for your reply. I'm using Materials Studio 7. I'm studying the dipole moment of (SO4)2-, I want to compare the dipole moment of sulphate in bulk solution and that on a charged surface. It turned out that the length of sulphate dipole moment in bulk solution is 0.07 e\AA, and can be up to 2.4 e\AA near the surface, if I have the correct unit. The dipole moment is pointing out from the sulfur atom.

All the best,
Jingjing
 
CarstenCarsten (Accelrys) 
Were do the charges come from?
I do not expect a dipole moment for SO4(2-) in vacuum for example.
jjbjjb
Hi Carsten
I have CaSO4 solution in contact with the a clay mineral, I do understand that sulphate in vacuum is non-polar, even the solution, it isn't polar at all? From my understanding, there isn't cutoff value for polar/non-polar dipole moment. Such as the C-H bond has very small dipole moment (~ 0.4D),  in most of cases, it's considered as a non-polar bond, tell me if I'm wrong. Thank you very much!

All the best,
Jingjing
CarstenCarsten (Accelrys) 
Where do the charges you use come from?
jjbjjb
Hi Carsten
I'm a little confused about your question. You are asking why sulphate is charged or the direction of the dipole moment? Sulphate is in an ionic solution, I think that's why it's charged. The dipole moment is pointing out from the sulfur.

All the best,
Jingjing 
CarstenCarsten (Accelrys) 
I want to know who the charges were calculated and which type of point charges are used.
jjbjjb
Hi Carsten
I got the forcefield parameters of sulphate from CVFF, I calculated nonbonded interactions, bond stretch and angle bend.

nonbonded
so          LJ_6_12       3.550000000000000       0.2502000000000000    
os          LJ_6_12       3.150000000000000       0.2002000000000000
bond stretch
so       os          HARMONIC    9000.0000    1.4900
angle bend
os       so       os          THETA_HARM   500.0000  109.4700


All the best,
Jingjing
CarstenCarsten (Accelrys) 
It does not tell something about charges.

Anyway a fully optimized sulfate anion in vacuum should have no dipole moment when CVFF charges are used.

The dipole moment which is observed then in BULK or solution comes from distortions of angles and bonds of the sulfate anion.

-> again which which charges do you use. If they are not from CVFF and for example charge equilibration (QEq) the charges depend on the environment and  the structure of the sulfate anion.

 
jjbjjb
Hi Carsten
Thanks for you reply. I did use the charges from CVFF. Here are the charges I copied from the force field.

so         S      32.06000  2.0000   0   0   0
os         O      15.99940 -1.0000   0   0   0

My system is a clay-liquid-clay structure. The solution in my system had high concentration of 0.2M, and it was constrained in a confined layer of 50A. Will these contribute to the dipole moment of sulphate? 

All the best,
Jingjing