added readme

README.md

@@ -1,2 +1,39 @@
 # DEHam
-Double Exchange Hamiltonian Complete Version
+
+Double Exchange Hamiltonian: Complete Version
+=============================================
+
+I. Compiling
+------------
+
+1. Export environment variables for PETSc and SLEPc
+```shell
+export PETSC_DIR=/usr/local/Cellar/petsc/3.6.3_4/real
+export SLEPC_DIR=/usr/local/Cellar/slepc/3.6.2_1/real/
+```
+
+2. Make the executable
+```shell
+make ex1
+```
+
+II. Using DEHam
+---------------
+
+1. The DEHam program requires an input file which 
+   has the topology of the Hamiltonian and the various parameters
+   as explained below in a sample inputfile:
+
+```python
+140					# The total number of determinants
+7					# The largest number of non-zero elements per row
+2					# The number of processors used in parallel
+1					# The number of holes
+0					# The isz (ms-1/2) value
+1,2,3,1,2,3,4,5,6,7	# The topology of the system is specified here
+2,3,4,8,7,6,5,6,7,8	# first and second line contain the two sites linked
+1,1,1,2,2,2,2,3,3,3	# third line contains the type of link (1 for t, J 2 for K and 3 for none)
+.1430,-0.20,0.0000	# The three types of links this line gives J, K
+.1430,-0.20,0.0000	# 
+-1.00,0.0,0.00		# This line gives t
+```