gww.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/gww.x - from package: quantum-espresso

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

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