Update lecture_4.md - formulated learning objectives

src/lecture_4.md

@@ -19,9 +19,9 @@ Exercises 9.2, 9.4, 10.1, 10.2, 11.2, 11.5
 
     After this lecture you will be able to:
 
-    - formulate equations of motion describing electrons and phonons in 1D.
+    - formulate equations of motion for electrons and phonons in 1D.
     - solve these equations to arrive at the corresponding dispersion relations.
-    - derive the group velocity, effective mass, and density of states from a dispersion relation.
+    - derive the group velocity, effective mass, and density of states from the dispersion relation.
 
 Last lecture:
 
@@ -257,7 +257,9 @@ Also a sanity check: when the energy is close to the bottom of the band, $E = E_
 
     After this lecture you will be able to:
 
-    - formulate equations of motion describing electrons and phonons in 1D when there is more than one degree of freedom per unit cell 
+    - formulate equations of motion for electrons or phonons in 1D for systems with more than one degree of freedom per unit cell.
+    - solve these equations to arrive at the dispersion relation.
+    - derive the group velocity, effective mass, and density of states.
     
 ### More hoppings in LCAO