gchem3d: 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/gchem3d - from package: gcu-bin

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

Error in other languages:
gchem3d: bevel nie gevind nie
gchem3d: comandă negăsită
gchem3d: comando não encontrado
gchem3d: commande introuvable
gchem3d: command not found
gchem3d: käsku ei ole
gchem3d: không tìm thấy lệnh
gchem3d: komanda nerasta
gchem3d: Kommando nicht gefunden.
gchem3d: kommandot finns inte
gchem3d: komut yok
gchem3d: nie znaleziono polecenia
gchem3d: níor aimsíodh an t-ordú
gchem3d: no se encontró la orden
gchem3d: no s'ha trobat l'ordre
gchem3d: opdracht niet gevonden
gchem3d: parancs nem található
gchem3d: perintah tidak ditemukan
gchem3d: príkaz nenájdený
gchem3d: příkaz nenalezen
gchem3d: команда не найдена
gchem3d: командата не е открита
gchem3d: 命令找不到
gchem3d: コマンドが見つかりません