# Input File Description

## Program: d3hess.x / PWscf / Quantum ESPRESSO (version: 7.2)

> ### TABLE OF CONTENTS

> > INTRODUCTION

> > &INPUT

> > > prefix | outdir | filhess | step

> ### INTRODUCTION

> >     Purpose of d3hess.x:
> >       This is a post processing program to compute second derivatives of D3 dispersion in QE.

> >       The d3hess.x program should be run after an scf or relax calculation.
> >       It reads the molecular geometry from the xml file in the outdir and save
> >       the second derivatives matrix in a file on the disk.
> >       Afterwords, phonon reads the file and add the D3 Hessian matrix to the dynamical matrix with the proper phase (q),
> >       to include dispersion effects on vibrational frequencies.

> >       The workflow is just:

> >             (1) do an SCF
> >             (2) run d3hess
> >             (3) run phonon

> >       Please note that filhess in d3hess input and dftd3_hess in phonon input, if given, should match.

> >     Structure of the input data:
> >     ============================

> >        &INPUT
> >          ...
> >        /

## Namelist: &INPUT

prefix | CHARACTER
Default: | 'pwscf'

>     prefix of input file produced by pw.x
>     (wavefunctions are not needed)

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outdir | CHARACTER
Default: | value of the `ESPRESSO_TMPDIR` environment variable if set; current directory ('./') otherwise

>     directory containing the input data, i.e. the same as in pw.x

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filhess | CHARACTER
Default: | 'prefix.hess'

>     output file where the D3 hessian matrix is written
>     (should match dftd3_hess keyword in phonon calculation)

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step | REAL
Default: | 1.d-3

>      step for numerical differentiation in a.u.

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This file has been created by helpdoc utility on Sat Mar 18 15:50:15 CET 2023.