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 :
cutoffMethod = "shifted_force";
electrostaticScreeningMethod = "damped";
cutoffRadius = 28;
dampingAlpha = 0.14159292;

The resultant electrostatic potential is:  -821667.68 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";
Revision:	1823
Committed:	Tue Jan 8 21:02:27 2013 UTC (12 years, 6 months ago) by gezelter
Content type:	text/plain
File size:	1087 byte(s)
Log Message:	Fixed a bug
#	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	gezelter	1768	cutoffMethod = "shifted_force";
22	gezelter	1342	electrostaticScreeningMethod = "damped";
23			cutoffRadius = 28;
24			dampingAlpha = 0.14159292;
25
26	gezelter	1823	The resultant electrostatic potential is: -821667.68 kcal / mol
27	gezelter	1342
28	gezelter	1390	To obtain values for the electrostatic potential in OpenMD, we add the
29	gezelter	1342	ELECTROSTATIC_POTENTIAL keyword to the end of the statFileFormat:
30
31			statFileFormat = "TIME\|TOTAL_ENERGY\|POTENTIAL_ENERGY\|KINETIC_ENERGY\|TEMPERATURE\|PRESSURE\|VOLUME\|CONSERVED_QUANTITY\|ELECTROSTATIC_POTENTIAL";