直接读取能带数据，然后用经验公式计算谱函数得到 

下一步计算一个费米面，在费米面上标定nesting波矢，以及计算CDW情况下的费米面

band_d = load("band_d.txt");
%Ed_line_Gamma_M = band_d(1:40);
Ed_line_M_K =  band_d(41:70);
Ed_line = band_d(1:70);
nk = 4000;
k = linspace(0,length(Ed_line),nk);
Ed = interp1(1:length(Ed_line),Ed_line,k,'spline');
nw = 2000;
w = linspace(-0.7,0.2,nw);
%w =  linspace(-0.8,0.2,nw);
Gammar1 = 0.005;
Gammar2 = 0.005;
delta = 0.03;
Ak_d = zeros(nw,nk);
hold on
for i=1:nw
    for j=1:nk
        sigma_d = -1i*Gammar1+delta*delta/(w(i)+Ed(j)+1i*Gammar2);
        Ak_d(i,j) = imag(sigma_d)/((w(i)-Ed(j)-real(sigma_d))^2+imag(sigma_d)^2);
    end
end
[X,Y] = meshgrid(k,w);
mesh(X,Y,-Ak_d/pi);
ylim([-0.7,0])
%xlim([1,20])