Re: [AMBER] PBSA focusing

From: Ray Luo, Ph.D. <ray.luo.uci.edu>
Date: Mon, 15 Apr 2013 16:54:43 -0700

Jesper,

So the fine grid spacing is 0.5 A, and the coarse grid spacing is 4 A.
NFOCUS = 2 so only these two grids are used.

The coarse grid would be twice as large as the solute geometry since
FILLRATIO = 2. The grid dimension would be computed by using the 4 A
spacing.

The fine grid only depends on the solute geometry and is independent
of FILLRATIO. Otherwise, what's the point of using focusing? It should
be a just bit larger than the solute by default.

Ray

On Mon, Apr 15, 2013 at 4:03 PM, Jesper Sørensen <jesorensen.ucsd.edu> wrote:
> Hi Ray,
>
> Thanks for the reply, just to clarify further...
> So if I specify a resolution of 0.5 (grid spacing) and a fill ratio of 2 in PBSA.in, and nfocus=2 and fscale=8. Then how does the focusing work.
>
> Is it the 2nd calculation (the focused on) that adheres to these specified parameters and then the first calculation also uses the same fill ratio and a grid spacing of 4 (0.5*8)?
>
> Best,
> Jesper
>
> On Apr 15, 2013, at 2:38 PM, "Ray Luo, Ph.D." <ray.luo.uci.edu> wrote:
>
>> Jesper,
>>
>> Grid spacing is the spacing gap (in Angstrom) between any two adjacent
>> grid points. The number of grid points per dimension apparently
>> depends on both the spacial dimension (in Angstrom) and the grid
>> spacing (in Angstrom).
>>
>> The FILLRATIO keyword controls the spacial dimension for the coarse
>> grid. The fine grid spacial dimension (in Angstrom) is set just a bit
>> larger than the solute of interest, by default. The NBUFFER keyword
>> can be used to customize the fine grid dimension, i.e. extra no. of
>> grid points to be added beyond that computed by the solute geometry
>> and grid spacing.
>>
>> Ray
>>
>> On Mon, Apr 15, 2013 at 2:06 PM, Jesper Sørensen <jesorensen.ucsd.edu> wrote:
>>> Hi all,
>>>
>>> I am trying to understand exactly what happens during a focusing calculation using PBSA.
>>>
>>> The keyword "fscale" says: Set the ratio between the coarse and fine grid spacings in an electrostatic focussing calculation. Default to 8.
>>>
>>> Does that mean that the dimensions of the grid (in angstroms) are the same, but the grid spacing on the second calculation is higher? In that case what is the advantage to not just calculating it with the higher grid spacing at the beginning? Is that calculation using the finer grid faster when better initial estimates are used from the coarser grid calculation?
>>>
>>> Or are the two calculations being done on differently sized grids, so that the fillratio is high in the first calculation, and the smaller in the second calculation?
>>>
>>>
>>> Best regards,
>>> Jesper
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>>
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Received on Mon Apr 15 2013 - 17:00:02 PDT
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