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# overlap (c42b1)

Overlap of Molecular Similarity

This is a maximum overlap method to investigate the structural

similarity of flexible molecules. The atoms are described as Gaussians

and the interaction energy between different molecules are basically

overlap integrals. The Gaussians can represent either volume or charge.

Alternatively, the overlap of the electrostatic potential is provided

yielding exponential form.

This method supports all CHARMM functionality, because it provides

just another energy term and forces for it. Only periodic boundaries and

VIBRAN are not supported.

Refercence: :Juneja, A; Riedesel, H; Hodoscek, M ; Knapp, EW

JOURNAL OF CHEMICAL THEORY AND COMPUTATION (2009) 5, 659-673

* Description | Description of the OVERLAP commands.

* Usage | How to use the OVERLAP method.

* Implementation | Implementation of the OVERLAP method

* Performance | Performance Issues

This is a maximum overlap method to investigate the structural

similarity of flexible molecules. The atoms are described as Gaussians

and the interaction energy between different molecules are basically

overlap integrals. The Gaussians can represent either volume or charge.

Alternatively, the overlap of the electrostatic potential is provided

yielding exponential form.

This method supports all CHARMM functionality, because it provides

just another energy term and forces for it. Only periodic boundaries and

VIBRAN are not supported.

Refercence: :Juneja, A; Riedesel, H; Hodoscek, M ; Knapp, EW

JOURNAL OF CHEMICAL THEORY AND COMPUTATION (2009) 5, 659-673

* Description | Description of the OVERLAP commands.

* Usage | How to use the OVERLAP method.

* Implementation | Implementation of the OVERLAP method

* Performance | Performance Issues

Top

SYNTAX and DESCRIPTION

======================

One command (OLAP) is used in several different forms to specify

everything.

To initialize the method use:

OverLAP NUMB <int> WEIGht <real> VOLW <real> CHAW <real> ESPW <real> -

WIDTh <real> GAMMa <real> WEPO <real>

NUMB <int> - how many subsystems do we have

WEIG <real> - weighting factor for the whole overlap term; it also

accounts to bring units to kcal/mol, default = 1.0

VOLW <real> - weighting factor for the volume overlap term,

default = 0.0

CHAW <real> - weighting factor for the partial atomic charge overlap

term, default = 0.0

ESPW <real> - weighting factor for the electrostatic potential

overlap term, default = 0.0

NOTE: Since all these three individual weighting factors default to 0.0,

the user has to specify at least one of them as a non-zero value, or the

program will bomb out because there is no overlap to calculate!

The overall overlap Hodgkin index is calculated according to the following

formula:

VOLW * H(volume) + CHAW * H(charge) + ESPW * H(e-s.pot)

H(total) = -------------------------------------------------------

VOLW + CHAW + ESPW

This way the overall Hodgkin index will be scaled between -1 and 1, no

matter what are the values of the individual weighting factors.

WIDT <real> - this value is used to scale all the atomic radii when

calculating volume or electrostatic potential overlap,

default = 1.0

GAMM <real> - gamma value for the electrostatic potential, default = 1.0

WEPO <real> - linear factor for the electrostatic potential,

default = 1.0

Before this initial OLAP command is called, WMAIN array should contain

partial atomic charges. In the course of initializing the overlap

subsystem, these charges will be copied from WMAIN to an internal array.

After the initialization, the user should load WMAIN with per-atom

weighting factors for the volume overlap (if the volume overlap is to be

used at all). The most simple way to do this is via:

SCALAR WMAIN SET 1

which will give equal weighting of 1.0 to all atoms. Be aware of the

commands that could alter WMAIN array so that these weighting factors

are lost before calculating the overlap energy term!

After initialization, subsystems should be defined using the following

command:

OLAP SYST <int> WEIG <real> SELE <selection factor> END

SYST <int> - the number of the subsystem being defined, should be

in range from 1 to the number given in the initialization

command (NUMB parameter)

WEIG <real> - weighting factor for the system being defined,

default = 1.0

SELE ... END - selection of atoms which constitute this system.

The memory usage for these selections of subsystems is specified

dynamically so there can be as many as one needs of these lines.

Do not forget to cancel all physical energy terms between subsystems

treated with the OLAP! This can be done using BLOCK command. Here is an

example for three subsystems:

BLOCK 3

CALL 2 SELE ... END

CALL 3 SELE ... END

COEF 1 2 0.0

COEF 1 3 0.0

COEF 2 3 0.0

END

[For more than several subsystems, there will be many ``COEF x y 0.0''

lines. This is something which may change, since specifying many block

commands may cause users to make errors.

Possible solutions:

1. When generating nonbond list check the following:

if ((nolap(i).gt.0).and.(nolap(j).gt.0))then

if (iolap(nolap(i)).ne.iolap(nolap(j))) then

these 2 atoms have to be excluded.

endif

endif

2. Or put the above in the exclusion list ??

3. or use block code - this works!

To check which atom is in which subsystem one can use:

OLAP PRINt

To print out individual forces and separate volume, charge and

electrostatic potential Hodgkin indices use:

OLAP DEBUg - turn on debugging

OLAP NODEbug - turn off debugging

NOTE: This produces huge output! Therefore, it is not recomended to turn

debugging on before a minimization or a dynamics run.

Weighting factors for the overlap terms (WEIG, VOLW, CHAW, ESPW) and

factors determining the shape of Gaussian and exponential functions

(WIDT, GAMMa, WEPO) can be changed via:

OLAP RESTart WEIG <real> VOLW <real> CHAW <real> ESPW <real> -

WIDT <real> GAMMa <real> WEPO <real>

For the description of OLAP REST parameters, see above the section on

initializing.

NOTE: When utilizung OLAP REST command, default values of all parameters

are not the previous ones, but the general defaults (VOLW=0, CHAW=0,

ESPW=0, WIDT=1, GAMM=1, WEPO=1)! Therefore, the user has to specify all

the non-default values again.

To turn off the overlap method completely, use:

OverLAP OFF

NOTE: This command also copies charges back to WMAIN!

SYNTAX and DESCRIPTION

======================

One command (OLAP) is used in several different forms to specify

everything.

To initialize the method use:

OverLAP NUMB <int> WEIGht <real> VOLW <real> CHAW <real> ESPW <real> -

WIDTh <real> GAMMa <real> WEPO <real>

NUMB <int> - how many subsystems do we have

WEIG <real> - weighting factor for the whole overlap term; it also

accounts to bring units to kcal/mol, default = 1.0

VOLW <real> - weighting factor for the volume overlap term,

default = 0.0

CHAW <real> - weighting factor for the partial atomic charge overlap

term, default = 0.0

ESPW <real> - weighting factor for the electrostatic potential

overlap term, default = 0.0

NOTE: Since all these three individual weighting factors default to 0.0,

the user has to specify at least one of them as a non-zero value, or the

program will bomb out because there is no overlap to calculate!

The overall overlap Hodgkin index is calculated according to the following

formula:

VOLW * H(volume) + CHAW * H(charge) + ESPW * H(e-s.pot)

H(total) = -------------------------------------------------------

VOLW + CHAW + ESPW

This way the overall Hodgkin index will be scaled between -1 and 1, no

matter what are the values of the individual weighting factors.

WIDT <real> - this value is used to scale all the atomic radii when

calculating volume or electrostatic potential overlap,

default = 1.0

GAMM <real> - gamma value for the electrostatic potential, default = 1.0

WEPO <real> - linear factor for the electrostatic potential,

default = 1.0

Before this initial OLAP command is called, WMAIN array should contain

partial atomic charges. In the course of initializing the overlap

subsystem, these charges will be copied from WMAIN to an internal array.

After the initialization, the user should load WMAIN with per-atom

weighting factors for the volume overlap (if the volume overlap is to be

used at all). The most simple way to do this is via:

SCALAR WMAIN SET 1

which will give equal weighting of 1.0 to all atoms. Be aware of the

commands that could alter WMAIN array so that these weighting factors

are lost before calculating the overlap energy term!

After initialization, subsystems should be defined using the following

command:

OLAP SYST <int> WEIG <real> SELE <selection factor> END

SYST <int> - the number of the subsystem being defined, should be

in range from 1 to the number given in the initialization

command (NUMB parameter)

WEIG <real> - weighting factor for the system being defined,

default = 1.0

SELE ... END - selection of atoms which constitute this system.

The memory usage for these selections of subsystems is specified

dynamically so there can be as many as one needs of these lines.

Do not forget to cancel all physical energy terms between subsystems

treated with the OLAP! This can be done using BLOCK command. Here is an

example for three subsystems:

BLOCK 3

CALL 2 SELE ... END

CALL 3 SELE ... END

COEF 1 2 0.0

COEF 1 3 0.0

COEF 2 3 0.0

END

[For more than several subsystems, there will be many ``COEF x y 0.0''

lines. This is something which may change, since specifying many block

commands may cause users to make errors.

Possible solutions:

1. When generating nonbond list check the following:

if ((nolap(i).gt.0).and.(nolap(j).gt.0))then

if (iolap(nolap(i)).ne.iolap(nolap(j))) then

these 2 atoms have to be excluded.

endif

endif

2. Or put the above in the exclusion list ??

3. or use block code - this works!

To check which atom is in which subsystem one can use:

OLAP PRINt

To print out individual forces and separate volume, charge and

electrostatic potential Hodgkin indices use:

OLAP DEBUg - turn on debugging

OLAP NODEbug - turn off debugging

NOTE: This produces huge output! Therefore, it is not recomended to turn

debugging on before a minimization or a dynamics run.

Weighting factors for the overlap terms (WEIG, VOLW, CHAW, ESPW) and

factors determining the shape of Gaussian and exponential functions

(WIDT, GAMMa, WEPO) can be changed via:

OLAP RESTart WEIG <real> VOLW <real> CHAW <real> ESPW <real> -

WIDT <real> GAMMa <real> WEPO <real>

For the description of OLAP REST parameters, see above the section on

initializing.

NOTE: When utilizung OLAP REST command, default values of all parameters

are not the previous ones, but the general defaults (VOLW=0, CHAW=0,

ESPW=0, WIDT=1, GAMM=1, WEPO=1)! Therefore, the user has to specify all

the non-default values again.

To turn off the overlap method completely, use:

OverLAP OFF

NOTE: This command also copies charges back to WMAIN!

Top

USAGE

=====

Since everything is flexible, I suggest to start with aligning the

systems to themself first. With this approach one gets the estimate of

the weights and radii which can be later used and improved in the

alignement process of different species.

It is sometimes usefull to exclude certain atoms from the alignement

procedure. The obvious procedure to do this is to use SCALar command

and assign the WMAIN array to zero. This can be done both before

OLAP initialization (thus setting atomic charges to zero and excluding

them from the charge and electrostatic potential overlap) and after

it (thus excluding atoms from the volume overlap).

USAGE

=====

Since everything is flexible, I suggest to start with aligning the

systems to themself first. With this approach one gets the estimate of

the weights and radii which can be later used and improved in the

alignement process of different species.

It is sometimes usefull to exclude certain atoms from the alignement

procedure. The obvious procedure to do this is to use SCALar command

and assign the WMAIN array to zero. This can be done both before

OLAP initialization (thus setting atomic charges to zero and excluding

them from the charge and electrostatic potential overlap) and after

it (thus excluding atoms from the volume overlap).

Top

IMPLEMENTATION

==============

This is a new area of research, and the user might want to play with

the different ``energy'' terms or formulas. The following is a

guideline to do that. Everything CHARMM related is separated from the

energy routines, so it should be easy for anyone to adjust the

formulas for the systems under investigation.

Because in general we may have one atom in several systems we need to

use the following data structure:

NOLAP(i), i=1, NATOM this is a vector of pointers to the IOLAP array.

IOLAP(i), i=1, NOLAP(NATOM) this is a vector which contains the information

to which subsystem each atom belongs to.

Then the loop for the overlap integrals would be like this:

do i = 1, natom

do j = 1, natom

do k = nolap(i),nolap(i+1)-1

ix=iolap(k)

if(ix.gt.0) then

do l = nolap(j), nolap(j+1)-1

jx=iolap(l)

if(jx.gt.0) then

ipt = (ix-1)*ix/2+jx ! this is not general case

s(ipt) = s(ipt) + gauss(i)*gauss(j)

endif

enddo

endif

enddo

enddo

enddo

The above is simplified model for illustration purposes only. For

details see the actual code. All the code for calculating overlap

energies and forces is in energy/eolap.src; command-line analysis is

in misc/olap.src. Also see fcm/olap.fcm.

The keyword to compile the method is ##OVERLAP.

IMPLEMENTATION

==============

This is a new area of research, and the user might want to play with

the different ``energy'' terms or formulas. The following is a

guideline to do that. Everything CHARMM related is separated from the

energy routines, so it should be easy for anyone to adjust the

formulas for the systems under investigation.

Because in general we may have one atom in several systems we need to

use the following data structure:

NOLAP(i), i=1, NATOM this is a vector of pointers to the IOLAP array.

IOLAP(i), i=1, NOLAP(NATOM) this is a vector which contains the information

to which subsystem each atom belongs to.

Then the loop for the overlap integrals would be like this:

do i = 1, natom

do j = 1, natom

do k = nolap(i),nolap(i+1)-1

ix=iolap(k)

if(ix.gt.0) then

do l = nolap(j), nolap(j+1)-1

jx=iolap(l)

if(jx.gt.0) then

ipt = (ix-1)*ix/2+jx ! this is not general case

s(ipt) = s(ipt) + gauss(i)*gauss(j)

endif

enddo

endif

enddo

enddo

enddo

The above is simplified model for illustration purposes only. For

details see the actual code. All the code for calculating overlap

energies and forces is in energy/eolap.src; command-line analysis is

in misc/olap.src. Also see fcm/olap.fcm.

The keyword to compile the method is ##OVERLAP.

Top

PERFORMANCE ISSUES

==================

(since the systems are usually small this is not so big issue)

Very probably the method is trivial to parallelize. The following

should take care of it:

In OLAPINT()

icalc=0

do i = 1, natom

do j = 1, natom

....

icalc=icalc+1

if(mod(icalc,numnod).eq.mynod) then

...

call fmgauss()

...

endif

....

enddo

enddo

This is a scheme for perfect load balance. However there is some loss

in olapsd, because it always does it for all atoms (it doesn't scale)

This way there is no additional communication involved!!!?

PERFORMANCE ISSUES

==================

(since the systems are usually small this is not so big issue)

Very probably the method is trivial to parallelize. The following

should take care of it:

In OLAPINT()

icalc=0

do i = 1, natom

do j = 1, natom

....

icalc=icalc+1

if(mod(icalc,numnod).eq.mynod) then

...

call fmgauss()

...

endif

....

enddo

enddo

This is a scheme for perfect load balance. However there is some loss

in olapsd, because it always does it for all atoms (it doesn't scale)

This way there is no additional communication involved!!!?