fd.x: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/fd.x - from package: quantum-espresso

You may install the required package with command yum install {package}

Error in other languages:
fd.x: bevel nie gevind nie
fd.x: comandă negăsită
fd.x: comando não encontrado
fd.x: commande introuvable
fd.x: command not found
fd.x: käsku ei ole
fd.x: không tìm thấy lệnh
fd.x: komanda nerasta
fd.x: Kommando nicht gefunden.
fd.x: kommandot finns inte
fd.x: komut yok
fd.x: nie znaleziono polecenia
fd.x: níor aimsíodh an t-ordú
fd.x: no se encontró la orden
fd.x: no s'ha trobat l'ordre
fd.x: opdracht niet gevonden
fd.x: parancs nem található
fd.x: perintah tidak ditemukan
fd.x: príkaz nenájdený
fd.x: příkaz nenalezen
fd.x: команда не найдена
fd.x: командата не е открита
fd.x: 命令找不到
fd.x: コマンドが見つかりません