g_dyecoupl: 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/g_dyecoupl - from package: gromacs

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

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