samples/Madelung/README.txt

Madelung Energy Sample Calculation

The sample in this directory provides a way of checking the value of
the Madelung Energy for a perfect crystal of NaCl.  The relevant
quantities are:

M (Madelung constant) = 1.74756
a (lattice constant)  = 5.65 Angstroms
q^2 / (4 pi e0 a)     = 58.77233   kcal / mol
M q^2 / (4 pi e0 a)   = 102.708173 kcal / mol

The file NaCl.md contains 8000 ions, so the total electrostatic energy
of the perfect crystal in this file should be:

V_electrostatic = -821665.38  kcal / mol

Using different electrostatic calculation methods, we can get quite
close to this value.

For example, with :
electrostaticSummationMethod = "shifted_force";
electrostaticScreeningMethod = "damped";
cutoffRadius = 28;
dampingAlpha = 0.14159292;
switchingRadius = 28;

The resultant electrostatic potential is:  -821667.88 kcal / mol

To obtain values for the electrostatic potential in OpenMD, we add the
ELECTROSTATIC_POTENTIAL keyword to the end of the statFileFormat:

statFileFormat = "TIME|TOTAL_ENERGY|POTENTIAL_ENERGY|KINETIC_ENERGY|TEMPERATURE|PRESSURE|VOLUME|CONSERVED_QUANTITY|ELECTROSTATIC_POTENTIAL";

Note: Converging the Madelung energy often requires quite the use of
very large cutoff distances (on the order of 28 Angstroms).  This can
result in extremely large neighbor lists, well beyond the size
normally encountered by OpenMD.  If you are interested in Madelung
energy calculations, you may need to recompile OpenMD after making
changes to the following parameters in
 
 src/UseTheForce/DarkSide/neighborLists.F90 :

    integer, save :: listMultiplier = 200
    integer, parameter :: maxAllocations = 25


This recompilation should not be required in future versions of OpenMD.
Revision:	1465
Committed:	Fri Jul 9 23:08:25 2010 UTC (15 years ago) by chuckv
Content type:	text/plain
File size:	1712 byte(s)
Log Message:	Creating busticated version of OpenMD
#	User	Rev	Content
1	gezelter	1342	Madelung Energy Sample Calculation
2
3			The sample in this directory provides a way of checking the value of
4			the Madelung Energy for a perfect crystal of NaCl. The relevant
5			quantities are:
6
7			M (Madelung constant) = 1.74756
8			a (lattice constant) = 5.65 Angstroms
9			q^2 / (4 pi e0 a) = 58.77233 kcal / mol
10			M q^2 / (4 pi e0 a) = 102.708173 kcal / mol
11
12			The file NaCl.md contains 8000 ions, so the total electrostatic energy
13			of the perfect crystal in this file should be:
14
15			V_electrostatic = -821665.38 kcal / mol
16
17			Using different electrostatic calculation methods, we can get quite
18			close to this value.
19
20			For example, with :
21			electrostaticSummationMethod = "shifted_force";
22			electrostaticScreeningMethod = "damped";
23			cutoffRadius = 28;
24			dampingAlpha = 0.14159292;
25			switchingRadius = 28;
26
27			The resultant electrostatic potential is: -821667.88 kcal / mol
28
29	gezelter	1390	To obtain values for the electrostatic potential in OpenMD, we add the
30	gezelter	1342	ELECTROSTATIC_POTENTIAL keyword to the end of the statFileFormat:
31
32			statFileFormat = "TIME\|TOTAL_ENERGY\|POTENTIAL_ENERGY\|KINETIC_ENERGY\|TEMPERATURE\|PRESSURE\|VOLUME\|CONSERVED_QUANTITY\|ELECTROSTATIC_POTENTIAL";
33
34			Note: Converging the Madelung energy often requires quite the use of
35			very large cutoff distances (on the order of 28 Angstroms). This can
36			result in extremely large neighbor lists, well beyond the size
37	gezelter	1390	normally encountered by OpenMD. If you are interested in Madelung
38			energy calculations, you may need to recompile OpenMD after making
39	gezelter	1342	changes to the following parameters in
40
41			src/UseTheForce/DarkSide/neighborLists.F90 :
42
43			integer, save :: listMultiplier = 200
44			integer, parameter :: maxAllocations = 25
45
46
47	gezelter	1390	This recompilation should not be required in future versions of OpenMD.