r7148 - /branches/rdc_analysis/physical_constants.py -- August 11, 2008 - 18:12

Author: bugman
Date: Mon Aug 11 15:37:06 2008
New Revision: 7148

URL: http://svn.gna.org/viewcvs/relax?rev=7148&view=rev
Log:
Wrote the pcs_constant() function to calculate the pseudocontact shift 
constant.


Modified:
    branches/rdc_analysis/physical_constants.py

Modified: branches/rdc_analysis/physical_constants.py
URL: 
http://svn.gna.org/viewcvs/relax/branches/rdc_analysis/physical_constants.py?rev=7148&r1=7147&r2=7148&view=diff
==============================================================================
--- branches/rdc_analysis/physical_constants.py (original)
+++ branches/rdc_analysis/physical_constants.py Mon Aug 11 15:37:06 2008
@@ -83,6 +83,39 @@
 
     # Calculate and return the value.
     return - mu0 / (4.0*pi) * gx * gh * h_bar / r**3
+
+
+# The pseudocontact shift constant.
+###################################
+
+def pcs_constant(T, Bo, r):
+    """Calculate the pseudocontact shift constant.
+
+    The pseudocontact shift constant is defined as::
+
+            mu0 15kT   1
+        d = --- ----- ---- ,
+            4pi Bo**2 r**3
+
+    where:
+        - mu0 is the permeability of free space,
+        - k is Boltzmann's constant,
+        - T is the absolute temperature,
+        - Bo is the magnetic field strength,
+        - r is the distance between the paramagnetic centre (electron spin) 
and the nuclear spin.
+
+
+    @param T:   The temperature in kelvin.
+    @type T:    float
+    @param Bo:  The magnetic field strength.
+    @type Bo:   float
+    @param r:   The distance between the two nuclei.
+    @type r:    float
+    """
+
+    # Calculate and return the value.
+    return mu0 / (4.0*pi) * 15.0 * k * T / Bo**2 / r**3
+
 
 
 # Gyromagnetic ratios.