N = 800.0
p1 = {1, 0, 0};
p2 = {0, 1, 0};
p3 = {0, 0, 1};
B = {0.0, 0, 200.0};
MV = Convert[(MN Milli
Tesla)/VacuumPermeability,Ampere/Meter]/(Ampere/Meter);

ClearAll[Simple]
Options[Simple] = {
Angleθ0 -> 0,
Angleϕ0 -> 0,
Field -> B,
Sat -> MN,
Int -> m0,
Energy -> 0,
Direction1 -> p1,
Direction2 -> p2,
Direction3 -> p3
};

Simple[OptionsPattern[]] := Module[
{
B = OptionValue[Field],
θ0 = OptionValue[Angleθ0],
ϕ0 = OptionValue[Angleϕ0],
MN = OptionValue[Sat],
m0 = OptionValue[Int],
En = OptionValue[Energy],
p1 = OptionValue[Direction1],
p2 = OptionValue[Direction2],
p3 = OptionValue[Direction3],
t, m, mx, my, mz, Be, M, M1, a1, a2, a3

},
a1 = Sin[θ0] Cos[ϕ0] p1(*{1,0,0}*);
a2 = Sin[θ0] Sin[ϕ0] p2(*{0,1,0}*);
a3 = Cos[θ0] p3(*{0,0,1}*);
m0 = {Sin[θ0] Cos[ϕ0], Sin[θ0] Cos[ϕ0],
Cos[θ0]};
m = {mx[t], my[t], mz[t]};
M = m/m0;
M1 = {a1, a2, a3};
Be = B - MN {0.0, 0.0, mz[t]};
En = -{Be.M1}
]

DensPlot =
DensityPlot[
N[Energy], {Angleθ0, 0, 180}, {Angleϕ0, 0, 360},
ColorFunction -> "SunsetColors", PlotLegends -> Automatic];

DensPlot