bands_FS.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 Debian possible default full paths are:

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

You may install the required package with command apt-get install {package}

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