Clear[Hmp$, "Hmp", m, n, p, Nmax, "[Psi]*"]
Nmax = 10.; (want 80)
Hmp = Table[0, {p, Nmax}, {m, Nmax}];
Chop[ReplacePart[
Hmp, {m_, p_} :> (p^2 [Pi]^2)/2 KroneckerDelta[m, p] +
2 Integrate[
Sin[m [Pi] [Chi]] Sin[p [Pi] [Chi]] V[[Chi]], {[Chi], 0,
1}]]]
Clear[Hmp$, "*Hmp*", m, n, p, Nmax, "\[Psi]*"]
Nmax = 10.; (*want 80*)
Hmp = Table[0, {p, Nmax}, {m, Nmax}];
Chop[ReplacePart[
Hmp, {m_, p_} :> (p^2 \[Pi]^2)/2 KroneckerDelta[m, p] +
2 Integrate[
Sin[m \[Pi] \[Chi]] Sin[p \[Pi] \[Chi]] V[\[Chi]], {\[Chi], 0,
1}]]]