temp = 0.8;

% 
% Code begins:
% --

close all;

VOL_MAX   = 5;
N_POINTS  = 1000;
DELTA_VOL = 0.2*(1/3);
vol   = linspace( (1/3)+DELTA_VOL, VOL_MAX, N_POINTS ); 
% clear VOL_MAX N_POINTS DELTA_VOL;
helmholtz = -(8/3)*temp*log( 3*vol - 1 ) - 3./vol;

figure; 

plot( vol, helmholtz, '-o' ); grid on;