How to create the share point 2013 date column in document library using power shell?

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SharePoint2013

how to create the share point 2013 date column in document library using power shell?

kindly help me

Regards,

What I have tried:

i tried the below two scripts , below script is working for list only , when i execute the below script i am getting the null reference exception.

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

$WebURL="http://portal.crescent.com/sites/Sales"
$ListName="Vendors"
$FieldName="Date of Contract"
$RequiredField=$false
 
#Get Objects
$Web = Get-SPWeb $WebURL
$List= $Web.Lists[$ListName]
 
$List.Fields.Add($FieldName,"DateTime", $RequiredField)

or

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

$WebURL="http://portal.crescent.com/sites/Sales"
$sList = $WebURL.GetList($listURL)
    $spFieldType = [Microsoft.SharePoint.SPFieldType]::Datetime

    $sList.Fields.Add("OpCo",$spFieldType,$true)

    $field = $sList.Fields["OpCo"]

    $field.DefaultValue = $slist.Title

    $field.Update()

    $sList.Update()