[数值问题] 代码结果一直为零

Program workfile
    Implicit none
    integer , parameter :: q = 1000
    real , parameter :: t1 = 3.12 , t2 = 0.29 , t3 = -0.0103
    complex , parameter :: i = (0, 1) , t0 = (0,0)
    real , parameter :: PI = acos(-1.0) , a0 = 1.42e-10
    real :: b1(2), b2(2) , a1(2) , a2(2) , m1 , m2
    real , allocatable :: k(:,:,:)
    complex :: f1 , f2
    integer :: x , y
    complex :: f1_kx, f1_ky, f2_kx, f2_ky

    allocate(k(2,q-1,q-1))
    b1 = [ 2*PI/a0*sqrt(3.0) , 2*PI/a0 ]
    b2 = [ 2*PI/a0*sqrt(3.0) , -2*PI/a0 ]
    a1 = [ a0*sqrt(3.0)/2 , a0/2 ]
    a2 = [ a0*sqrt(3.0)/2 , -a0/2 ]
    Forall(x=1:size(k,2), y=1:size(k,3))
            k(:,x,y) = (b1*x+b2*y)/q
    End Forall
!    print*,k(:,1,2)
    m1 = dot_product(a1 , k(:,1,2))
    m2 = dot_product(a2 , k(:,1,2))
    f1 = 1+exp(i*m1)+exp(i*m2)
    f2 = 1+exp(-i*m1)+exp(-i*m2)

call diff(i,a0,k(1,1,2),k(2,1,2))
print *, f1_kx,f1_ky, f2_kx, f2_ky

contains
subroutine diff(i,a,x,y)
        implicit none
        real,intent(in) :: a, x, y
        complex :: i, f1_kx, f1_ky, f2_kx, f2_ky
        f1_kx = (sqrt(3.0)/2)*a*i*exp(a*i*(sqrt(3.0)*x/2+y/2))+(sqrt(3.0)/2)*a*i*exp(a*i*(sqrt(3.0)*x/2-y/2))
        f2_kx = -(sqrt(3.0)/2)*a*i*exp(a*i*(sqrt(3.0)*x/2+y/2))-(sqrt(3.0)/2)*a*i*exp(a*i*(sqrt(3.0)*x/2-y/2))
        f1_ky = (-1/2)*a*i*exp(a*i*(sqrt(3.0)*x/2-y/2))+(1/2)*a*i*exp(a*i*(sqrt(3.0)*x/2+y/2))
        f2_ky = (1/2)*a*i*exp(a*i*(sqrt(3.0)*x/2-y/2))-(1/2)*a*i*exp(a*i*(sqrt(3.0)*x/2+y/2))
        return
endsubroutine

  (0.00000000,0.00000000)             (0.00000000,0.00000000)             (0.00000000,0.00000000)             (0.00000000,0.00000000)

   78 | subroutine diff(i,a,x,y)
      |                 1
Error: Symbol ‘i’ at (1) has no IMPLICIT type
workfile_ed4.f90:73:33:

   73 | call diff(i,a0,k(1,1,2),k(2,1,2))
      |                                 1
Error: Type mismatch in argument ‘i’ at (1); passed COMPLEX(4) to UNKNOWN