[gmx-users] Charges in vacuum simulation

2013-10-28 Thread Richa Singh
Hi all,

I'm trying to run a vacuum simulation of my protein which has a non-zero charge.
How to deal with this charge? Can I add counter ions in to my system?
Would it be energetically stable?

How can one bring a protein to its isoelectric point?
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Re: [gmx-users] Charges in vacuum simulation

2013-10-28 Thread Dr. Vitaly Chaban
If in vacuum, I would add hydrogens via covalent bonds.

Dr. Vitaly V. Chaban


On Mon, Oct 28, 2013 at 10:29 AM, Richa Singh
richa.s.rathor...@gmail.com wrote:
 Hi all,

 I'm trying to run a vacuum simulation of my protein which has a non-zero 
 charge.
 How to deal with this charge? Can I add counter ions in to my system?
 Would it be energetically stable?

 How can one bring a protein to its isoelectric point?
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[gmx-users] Charges for calculation of Coulomb interaction

2013-04-11 Thread fantasticqhl

Dear GMX users,

Just a simple question, are the Coulomb interactions  calculated using 
charges from ffnonbonded.itp or aminoacid.rtp?


Normally, they are the same. However, if I modify some charges for some 
atoms (for example CB) of some residues in the aminoacid.rtp,
but do not modify in ffnonbonded.itp because some other residues would 
still used the old charges, how will gromacs treat the calculations?
Right now I know the best option is introducing new atom types. Thanks 
very much!


All the best,
Qinghua

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Re: [gmx-users] Charges for calculation of Coulomb interaction

2013-04-11 Thread Justin Lemkul
On Thu, Apr 11, 2013 at 5:09 AM, fantasticqhl fantastic...@gmail.comwrote:

 Dear GMX users,

 Just a simple question, are the Coulomb interactions  calculated using
 charges from ffnonbonded.itp or aminoacid.rtp?

 Normally, they are the same. However, if I modify some charges for some
 atoms (for example CB) of some residues in the aminoacid.rtp,
 but do not modify in ffnonbonded.itp because some other residues would
 still used the old charges, how will gromacs treat the calculations?
 Right now I know the best option is introducing new atom types. Thanks
 very much!


Charges from ffnonbonded.itp are never read.

-Justin

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Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
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231-9080http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin


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Re: [gmx-users] Charges for Coulomb potential

2012-08-30 Thread Delmotte, Antoine

Alright, I understand now.

Many thanks for this!

Antoine

Le 29/08/2012 18:57, Mark Abraham a écrit :

On 30/08/2012 3:18 AM, Delmotte, Antoine wrote:

Many thanks for your quick response, Mark.

So epsilon_r is actually different from the actual relative 
permittivity (which would be like 80 for water), is that right?


You can have an atomistic solvent or a continuum solvent, but not both 
at once.




If so, how does one usually chooses this value of epsilon_r? Is the 
default value of 1 applicable for most cases (like for simulations in 
water), or should one obtain it from the literature somehow?


The force field defines it (normally to 1).

Mark



Thank you,

Antoine

On 29/08/12 14:47, Mark Abraham wrote:

On 08/29/2012 11:08 PM, Delmotte, Antoine wrote:

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb 
potential:


E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file aminoacids.rtp of 
the force field used?


If you use pdb2gmx to generate your .top, yes. More generally, 
GROMACS uses the charges found in the .top.


Could you also please redirect me towards the relevant literature 
for the calculation of epsilon_r in Gromacs?  (or does Gromacs uses 
a fixed epsilon_r?)


You choose it. See parts of manual 4.1 and 7.3

Mark






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[gmx-users] Charges for Coulomb potential

2012-08-29 Thread Delmotte, Antoine

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb potential:


E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file aminoacids.rtp of the 
force field used?


Could you also please redirect me towards the relevant literature for 
the calculation of epsilon_r in Gromacs?  (or does Gromacs uses a fixed 
epsilon_r?)


Thank you very much in advance,

Antoine
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Re: [gmx-users] Charges for Coulomb potential

2012-08-29 Thread Mark Abraham

On 08/29/2012 11:08 PM, Delmotte, Antoine wrote:

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb 
potential:


E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file aminoacids.rtp of the 
force field used?


If you use pdb2gmx to generate your .top, yes. More generally, GROMACS 
uses the charges found in the .top.


Could you also please redirect me towards the relevant literature for 
the calculation of epsilon_r in Gromacs?  (or does Gromacs uses a 
fixed epsilon_r?)


You choose it. See parts of manual 4.1 and 7.3

Mark
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Re: [gmx-users] Charges for Coulomb potential

2012-08-29 Thread Delmotte, Antoine

Many thanks for your quick response, Mark.

So epsilon_r is actually different from the actual relative permittivity 
(which would be like 80 for water), is that right?


If so, how does one usually chooses this value of epsilon_r? Is the 
default value of 1 applicable for most cases (like for simulations in 
water), or should one obtain it from the literature somehow?


Thank you,

Antoine

On 29/08/12 14:47, Mark Abraham wrote:

On 08/29/2012 11:08 PM, Delmotte, Antoine wrote:

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb 
potential:


E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file aminoacids.rtp of 
the force field used?


If you use pdb2gmx to generate your .top, yes. More generally, GROMACS 
uses the charges found in the .top.


Could you also please redirect me towards the relevant literature for 
the calculation of epsilon_r in Gromacs?  (or does Gromacs uses a 
fixed epsilon_r?)


You choose it. See parts of manual 4.1 and 7.3

Mark


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Re: [gmx-users] Charges for Coulomb potential

2012-08-29 Thread Mark Abraham

On 30/08/2012 3:18 AM, Delmotte, Antoine wrote:

Many thanks for your quick response, Mark.

So epsilon_r is actually different from the actual relative 
permittivity (which would be like 80 for water), is that right?


You can have an atomistic solvent or a continuum solvent, but not both 
at once.




If so, how does one usually chooses this value of epsilon_r? Is the 
default value of 1 applicable for most cases (like for simulations in 
water), or should one obtain it from the literature somehow?


The force field defines it (normally to 1).

Mark



Thank you,

Antoine

On 29/08/12 14:47, Mark Abraham wrote:

On 08/29/2012 11:08 PM, Delmotte, Antoine wrote:

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb 
potential:


E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file aminoacids.rtp of 
the force field used?


If you use pdb2gmx to generate your .top, yes. More generally, 
GROMACS uses the charges found in the .top.


Could you also please redirect me towards the relevant literature 
for the calculation of epsilon_r in Gromacs?  (or does Gromacs uses 
a fixed epsilon_r?)


You choose it. See parts of manual 4.1 and 7.3

Mark




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[gmx-users] charges

2012-04-02 Thread R.Perez Garcia
Dear GROMACS users,
I would like to place the charge more localized in the bonds region and not 
exactly in the atoms.
Please let me know if you know there is a way to do this in GROMACS.
Thank you in advance, R 
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Re: [gmx-users] charges

2012-04-02 Thread David van der Spoel

On 2012-04-02 20:29, R.Perez Garcia wrote:

Dear GROMACS users,
I would like to place the charge more localized in the bonds region
and not exactly in the atoms.
Please let me know if you know there is a way to do this in GROMACS.
Thank you in advance, R



Yes, using virtual sites.
There's an expert group of gromacs users at the department of 
biophysical chemistry at your university, Marrink. You may want to talk 
to then.


--
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell  Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205.
sp...@xray.bmc.uu.sehttp://folding.bmc.uu.se
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Re: [gmx-users] charges

2012-04-02 Thread R.Perez Garcia
Dear prof. van der Spoel,
I know.. Dr. Alex de Vries is supervising me for my colloquium. Unfortunately 
(for me), they are very busy and (mainly) I am doing four months stage at 
Perugia universityv (It) which means I can not personally ask...so I prefer to 
ask the list.
Thank you for your answer, even if the literature concerning virtual charges is 
not a lot, I will keep looking.
Best regards: R

On 02-04-12, David van der Spoel  sp...@xray.bmc.uu.se wrote:
 On 2012-04-02 20:29, R.Perez Garcia wrote:
 Dear GROMACS users,
 I would like to place the charge more localized in the bonds region
 and not exactly in the atoms.
 Please let me know if you know there is a way to do this in GROMACS.
 Thank you in advance, R
 
 
 Yes, using virtual sites.
 There's an expert group of gromacs users at the department of biophysical 
 chemistry at your university, Marrink. You may want to talk to then.
 
 -- 
 David van der Spoel, Ph.D., Professor of Biology
 Dept. of Cell  Molec. Biol., Uppsala University.
 Box 596, 75124 Uppsala, Sweden. Phone:+46184714205.
 sp...@xray.bmc.uu.se    http://folding.bmc.uu.se
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Re: [gmx-users] charges

2012-04-02 Thread David van der Spoel

On 2012-04-02 20:40, R.Perez Garcia wrote:

Dear prof. van der Spoel,
I know.. Dr. Alex de Vries is supervising me for my colloquium.
Unfortunately (for me), they are very busy and (mainly) I am doing four
months stage at Perugia universityv (It) which means I can not
personally ask...so I prefer to ask the list.
Thank you for your answer, even if the literature concerning virtual
charges is not a lot, I will keep looking.
Best regards: R


It's in the manual.
[ virtual_sites2 ]
; k i j type constant
3  1 2 1  0.5

will give you a virtual site 3 half-way atoms 1  2.



On 02-04-12, *David van der Spoel * sp...@xray.bmc.uu.se wrote:

On 2012-04-02 20:29, R.Perez Garcia wrote:
Dear GROMACS users,
I would like to place the charge more localized in the bonds region
and not exactly in the atoms.
Please let me know if you know there is a way to do this in GROMACS.
Thank you in advance, R


Yes, using virtual sites.
There's an expert group of gromacs users at the department of
biophysical chemistry at your university, Marrink. You may want to
talk to then.

--
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell  Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone: +46184714205.
sp...@xray.bmc.uu.se http://folding.bmc.uu.se
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David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell  Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205.
sp...@xray.bmc.uu.sehttp://folding.bmc.uu.se
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[gmx-users] Charges

2011-02-11 Thread Tanos Franca

Dear gmx users,
Does someone know in which file GROMACS store the information on 
the protein charge. I've seen that after running pdb2gmx or grompp the 
system charge is shown in the screen but we would like to know if this 
information is recorded in some file.

With my best regards,
Tanos C. C. Franca.
Coordinator of the Graduate Program in Chemistry.
Military Institute of Engineering
Rio de Janeiro - RJ
Brazil.
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Re: [gmx-users] Charges

2011-02-11 Thread Justin A. Lemkul



Tanos Franca wrote:

Dear gmx users,
Does someone know in which file GROMACS store the information on the 
protein charge. I've seen that after running pdb2gmx or grompp the 
system charge is shown in the screen but we would like to know if this 
information is recorded in some file.


It's in your topology.  The qtot entry keeps a running total of the charge on 
the protein.  The last line in [atoms] indicates the overall net charge.


-Justin


With my best regards,
Tanos C. C. Franca.
Coordinator of the Graduate Program in Chemistry.
Military Institute of Engineering
Rio de Janeiro - RJ
Brazil.


--


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin


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[gmx-users] Charges in SW water model

2008-11-20 Thread Andreas Kring

Dear Professor Spoel.

I have a question concerning your article on the SW water model 
published in J. Phys. Chem. B, 105, 2618-2626 (2001). I guess the 
question is only indirectly related to GROMACS, but I'll post in on the 
mailing list since it may be of interest to other GROMACS users as well.


Equation (4) of the paper states that

k_nn = (q_s)^2/alpha_nn,

where nn is either xx, yy or zz. k is the spring constant, q_s is the 
charge and alpha is the polarizability. The first line in section 2.2 of 
the paper is After determining the charges and spring constants 
corresponding to the polarizabilities It seems as if the are too 
many unknowns in the equation above, or do I miss something?


If I understand it correctly, the spring constants are determined from 
q_s and alpha. But how is the charge determined?


Hope you can help with this question.

Kind regards
Andreas

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[gmx-users] Charges?

2007-03-01 Thread Triguero, Luciano O
Hi gromacs guru!

Does any know a clever way on how to convert QM charges to group charges as in 
shown in the residue topology file?

Ciao,

Luciano

Dr. Luciano Triguero
College of Art and Science
Department of Chemistry
Cox Science Building
1301 Memorial Drive, Room 146
P.O Box 249118
Coral Gables, FL 33124-0431
Cellular: 305-904-2419
Office: 305-284-3938

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Re: [gmx-users] Charges?

2007-03-01 Thread Mark Abraham

Triguero, Luciano O wrote:

Hi gromacs guru!

Does any know a clever way on how to convert QM charges to group charges as in 
shown in the residue topology file?


Nope. You should read the documentation for the force field - probably 
the original published manuscript - and see how the others were 
developed, and try to do something consistent. There's no reason to 
expect a correlation between charges calculated with an arbitrary QM 
method and the partial charge *optimized parameters* used in an 
arbitrary MM force field.


Mark
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[gmx-users] charges for non-natural residues with gromos 53a6

2006-12-07 Thread Carsten Baldauf

dear all//
i need to parameterize a non-natural amino acid residue.
i have a problem with assigning the charges, how should i scale them? i 
can obtain quantum chemical charges from AM1 to {HF,DFT}/6-31G* and 
further, but how to include (scaling, i now where to write them) them in 
the force field?

thanks a lot//
carsten


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[gmx-users] charges for non-natural residues with gromos 53a6

2006-12-07 Thread Carsten Baldauf

the problems gets more difficult to me ... :-(

i want to substitute a single peptide bond in a normal sequence with an 
ester bond. i have problems finding the right parameters for an ester 
bond, does somebody has done something similar? i would be very happy 
about any help.

thanks in advance//
carsten

dear all//
i need to parameterize a non-natural amino acid residue.
i have a problem with assigning the charges, how should i scale them? i
can obtain quantum chemical charges from AM1 to {HF,DFT}/6-31G* and
further, but how to include (scaling, i now where to write them) them in
the force field?
thanks a lot//
carsten


--
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[gmx-users] charges in polymer

2006-11-27 Thread Dmitriy Golubobsky

Dear Guru,
i need an advice.
i create 3 resudues for my polymer. ( begin-monomer, middle-monomer,
end-monomer)
optimize geometry and charges in gaussin 6-31G.
formalize topology for OPLS force-field.
but, i've got a question
have i to do RESP of the charges of my monomers according to ff or not?
if yes, what have i to use for it.
Thank you.

--
Dmitriy Golubovsky
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Re: [gmx-users] charges in polymer

2006-11-27 Thread Mark Abraham

Dmitriy Golubobsky wrote:

Dear Guru,
i need an advice.
i create 3 resudues for my polymer. ( begin-monomer, middle-monomer, 
end-monomer)

optimize geometry and charges in gaussin 6-31G.
formalize topology for OPLS force-field.
but, i've got a question
have i to do RESP of the charges of my monomers according to ff or not?
if yes, what have i to use for it.


If you are extending a force field, read how they developed that force 
field and do something consistent. The above looks more like you are 
making something up entirely, in which case do whatever you like, but 
you've got a better chance of getting past referees if you either use 
something close to an existing methodology or demonstrate its 
effectiveness by comparison with existing simulations or experiments.


Mark
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