“…Moreover, suppose f is asymptotically periodic in x in the following sense, and there exists a continuous function f p ( x , u ) on , which is 1‐periodic in each component x j (1 ≤ j ≤ N) of x , such that - is strictly increasing on ( − ∞ ,0) and (0, ∞ ),
- | f ( x , u ) | ≥ | f p ( x , u ) | , ,
- | f ( x , u ) − f p ( x , u ) | ≤ | h ( x ) | ( | u | + | u | q ), , , where is the class of functions such that, for every ϵ > 0 the set has finite Lebesgue measure.
Theorem If (H 1 )–(H 8 ) hold, then the problem (NLS) has a ground state solution. Remark In, f ( x , u ) is asymptotically periodic in x if there is a periodic function f p such that …”