# Variables
r_na = 0.98; #ionic radius of sodium in angstorm
r_cl = 1.81; #ionic radius of chlorine in angstorm
n = 4.; #in fcc there are 4 Na and 4 Cl ions
# Calculations
a = ((2*r_na)+(2*r_cl)); #latice constant
apf = ((n*(4./3)*3.14*r_na**3)+(n*(4./3)*3.14*r_cl**3))/a**3;
# Results
print "Lattice consmath.tant = ",a
print "atomic packing fraction of NaCl having FCC structure = %.2f"%apf
import math
# Variables
r = 1.278; #radius of copper in angstorm
#copper has FCC structure
a = round(4*r/math.sqrt(2),2); #in angstorm
a1 = a*10**-8; #in cm
aw = 63.54; #atomic weight of copper
ne = 4.; #fcc
na = 6.023*10**23; #Avagadro's no.
p = aw*ne/(na*a1**3); #in g/cm**3
# Results
print "a (in Angstorm) = %.2f A"%a
print "Density of Copper (in gm/cm**3) : %.2f"%p
# Variables
w_na = 23.; #atomic weight of Na
w_cl = 35.5; #atomic weight of Cl
w = w_na+w_cl; #effective no.of atoms in FCC structure
n = 4.; #FCC
# Calculations
na = 6.023*10**23; #Avagadrro's no.
w_4 = w*n/na; #weight of 4 molecules in gm
p = 2.18; #density in gm/cm**3
a3 = (w*n)/(na*p)
a = a3**(1./3)
#a = (w_4/p)**(1/3); #in cm
a1 = a*10**8; #in angstorm
d = a1/2;
# Results
print "unit cell dimension (in angstorm) = %.2f A"%a1
print "Distance between two adjacent atoms (in Angstorm) = %.2f A"%d
# Variables
n = 2.; #BCC
p = 7.86; #density in gm/cm**3
aw = 55.85; #atomic weight of iron
# Calculations
na = 6.023*10**23; #Avagadrro's no.
a = ((aw*n)/(na*p))**(1./3); #in cm
a1 = a*10**8; #in angstorm
r = math.sqrt(3)*a1/4;
# Results
print "unit cell dimension of iron (in angstorm) = %.2f A"%a1
print "atomic radius = %.3f A"%r