When calculating the momentum relaxation time using the following line in the transport.f90 of QE-6.8

Code: Select all

```
vel_factor(ibnd, jbnd) = DDOT(3, vkk(:, ibnd), 1, vkq(:, jbnd), 1) / &
DDOT(3, vkk(:, ibnd), 1, vkk(:, ibnd), 1) (Eq. 1)
```

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```
vel_factor(:, :) = one - vel_factor(:, :) (Eq. 2)
```

Eq. 2 then makes the final vel_factor negative which in turn makes the scattering rates for those kpoints negative.

Is there a way these negative rates could be avoided?

One possible solution is to use the following instead of Eq. 1

Code: Select all

```
vel_factor(ibnd,jbnd) = DDOT(3, vkk(:,ibnd), 1,vkq(:,jbnd), 1) / &
(abs(SQRT(DDOT(3, vkk(:,ibnd), 1,vkk(:,ibnd),1)))* &
abs(SQRT(DDOT(3, vkq(:,jbnd), 1,vkq(:,jbnd),1))) ) (Eq. 3)
```

I would appreciate any input in this matter.

Thank you,

Vahid

Vahid Askarpour

Department of physics and atmospheric science

Dalhousie University

Halifax, NS

CANADA